Assembly Instructions AC-30 Audio Cassette Interface
Contents
1. recorder and depress the REWIND butto depress the PLAY button to advance several seconds beyond the leader on the tape Stop the recorder and this time depr the RECORD status switch to set the RECORD status light ON Then enter a P for punch on the terminal s keyboard tarting location of the program Now use the should be set for manual motor control with the RECORD READ status switches in the center position with the status lights nut and the LOCAL REMOTE switch in the REMOTE position Load a blank or previously erased tape into the selected cassette n to get to the beginning of the tape Then The record DATA light will flic tape When the dump is completed the ss the cassette recorder RECORD button Flip ker as program data is stored to the cassette DATA light will go out Do not stop the recorder instead set memory locations A002 thru A005 to dump the data stored in the program counter storage addresses as well Since the record STATUS light is lit this data passing back and forth betw the still operating recorder but is however ignored when loading the program Again enter a P for punch The DATA light w a second since only two memory locations are written to the tape Now while the cassette recorder is still recording flip the LOCAL REMOTE switch to the LOCAL position and type in on the terminal s keyboard S9 You can only type the S9 if you have the 16X baud rate clock fed fro2. Interface on I 0 card slot 1 are of no use to us On top of that the standard MP S serial interface option does not have enough control lines available to provide READER ON READER OFF RECORD ON and RECORD OFF logic control for the attached AC 30 Cassette Interface For these reasons it is our recommendation that the AC 30 be interfaced to the computer system thru a separate MP C Control Interface configured for 300 baud located at some unused I 0 card position on the interface buss This means there will be a larger overhead in software for the user but the extra unused parallel lines on the parallel PIA integrated circuit may be used for AC 30 READER ON READER OFF RECORD ON and RECORD OFF control functions Our cassette version of the Editor Assembler software already has I 0 routines contained within to drive an MP C Control Interface located at any I 0 card position on the SWTPC 6 00 Computer System READER ON READER OFF RECORD ON and RECORD OFF control commands may be taken off unused pins on the PIA parallel interface chip The lines have been assigned on the control interface when using the Editor Assembler software package It is suggested that you use the same assignments to maintain consistency To actually use these logic control lines within your own programming you will have to write routines within your
3. own cassette I 0 software package to put a TTL compatible 1 to 1000 microsecond negative going strobe pulse on the respective PIA pin to generate the desired command A connector is attached from these MP C PIA pins to the control lines on the AC 30 Cassette Interface and is installed as follows Make the connections from the indicated pins of ICI on the MP C Control Interface board to the specified pins of a twelve pin male connector shell Be sure to make the wires long enough to reach your AC 30 Cassette Interface where th connector will be plugged FROM TO P C ICI pin 7 12 pin male sh female pin 1 pin 4 12 pin male sh female pin 2 pin 6 12 male sh female pin 3 5 12 pin male sh female pin 4 Terminal s 16X clock OUT 12 pin male sh female pin 5 Terminal s 16X clock IN 12 pin male sh female pin 6 ground 12 pin male sh female pin 12 The mating connector on the AC 30 Cassette Interface should be installed just as is shown in the interconnection drawing for the SWTPC 6800 and CT 1024 Terminal System Other connections are made as shown in the appropriate block diagram All data connections made to the AC 30 should be thru the connector provided for the computer Since there will be no terminal connected directly to the AC 30 there is of course no LOCAL mode of o
4. should be TTL compatible pulses between 1 and 1000 microseconds duration The logic is set up for negative going pulses however grounding the CONTROL INVERT line on the AC 30 board programs the AC 30 for positive going pulses If you are forced to use the cassette control logic put out on the SWTPC 6800 s MP C Control Interface board by the Editor Assembler software make the following connections from the indicated pins of on the MP C Control Interface board to the specified pins of a twelve pin male connector shell Be sure to make the wires long enough to reach your AC 30 Cassette Interface where the connector will be plugged If you do have access to your terminal s 16X baud rate clock the terminal s clock buss should be broken and the 16X clock OUT and 16X clock IN lines brought out to the same connector FROM TO P C pin 7 12 pin male sh female pin 1 pin 4 12 pin male sh female pin 2 pin 6 12 pin male sh female pin 3 P C 5 12 pin male sh female pin 4 Terminal s 16X clock OUT 12 pin male sh female pin 5 Terminal s 16X clock IN 12 pin male sh female pin 6 ground 12 pin male sh female pin 12 The mating connector on the 30 Cassette Interface as w
5. switch actually determines th the MANUAL position both always activated thru off the interface s sel function of the the record and their respective REMOTE marking carrier even computer and terminal computer or manual control terminal is simultaneously transmitted out t if there is data flowi AS soon as the record record and read status latches In read cassette recorder motors are jacks If the record latch is cted recorder MIC jack will output a constant ng back and forth between the latch is turned on either by the all data transmitted from the computer to the hru this same MIC jack Data flow out of the MIC jack ceases as soon as the record latch is again reset by either manual or computer control If the read latch is off the interface will ignor all data incoming thru its selected EAR jack and yet pass data back and forth between the If the read latch is turned ON either by manual or computer control and valid audio tones are sensed read data is stored from the cassette unit to the simultaneously displayed on the attached terminal is programmed to echo the incoming cassette data terminal and computer to the computer system ceases audio tones on the tape from the selected EAR jack computer This same data is system only if the computer Data flow from the cassette ither upon resetting the read latch or loss of Operation in the AUTO
6. the board any more than necessary and when you must avoid touching or allowing anything to come into contact with any of the conductors on the board Parts List AC 30 Audio Cassette Interfac R1 R2 R3 R9 R11 R12 R15 R19 R22 R27 R29 R32 R34 R36 R40 R42 R44 R47 R4 R48 R49 R5 R6 R7 R30 R31 R35 R37 R43 R8 R17 R18 R23 R26 R10 R13 R14 R16 R38 R39 C1 66 561256155 C2 G3 C9 C4 C5 C18 C7 G9 C10 C11 19 C20 CLO C22 C17 C21 C2370295 ICI ECS TCZ ICI ICA 6 4 9 0 12 5 6 D1 D2 D4 05 011 D3 212 D13 D14 D17 D18 D22 Ql Q2 04 08 03 09 011 Resistors 33K ohm 1 4 watt resistor 10K ohm 1 4 watt resistor 10K ohm 1 4 watt resistor 10K ohm 1 4 watt resistor 330 ohm 1 4 watt resistor 2 2K ohm 1 4 watt resistor 4 47 100K ohm 1 4 w 330K ohm 1 4 w 22 20K ohm trimme 47 7K ohm 1 4 w 0 ohm 1 4 wa tt resistor t resistor tt resistor tt resistor t resistor resistor t resistor K ohm 1 4 wa 0 2 0 OK CQ Er ch ck cb ct K ohm 1 4 wa 200K ohm trimmer resistor Capac itors 1000 pfd capacitor 2000 pfd capacitor 0 1 0 0 27 47 10 10 10 0 022 mfd capacitor mfd 15 VDC electrolytic capacitor 01 mfd capacitor 047 mfd capacitor 00 pfd capacitor 0 pfd capacitor 0 mfd 16 VDC electrolytic capa
7. this header data is read The cassette interface is more vulnerable to error reads between incrementally recorded data than at any other time Th nd of each data block may easily be detected by recording some non displayed control character at the end of each data block If you are using the cassette interface with the SWTPC 6800 Computer system and CT 1024 TV Typewriter II terminal system the decoded RECORD OFF ASCII Control T command 1446 not only turns the recorder off but is written at the end of the data record as well for an end of record character Incrementally recorded records may be read either continuously or incremen tally In either case you must provide a software delay in your program at least one character time 33 milliseconds between the time th nd of record character is read and the time data is output from the interface The reason being that there is a slight delay between the loss of carrier on the tape and action of the CARRIER DETECT circuitry which in turn creates a gap in the 16 X UART clock This gap 6 auses problems so long as you not outputting data during the clock thus he reason for the delay Fortunately all of the formentioned considerations are only necessary when using the interface in the incremental start stop mode Operating the system in the continuous motor control disabled mode isn t much different from paper t
8. turn the computer off just to make sure the memory resident program is destroyed befor loading Reapplying power will force an auto reset and bring up the resident MIKBUG firmware on the SWTPC 6800 Rewind the tape to the beginning make sure the cassette recorder s volume is set to a reliable setting and depress the play button Then type in a L for load on the terminal s keyboard The read STATUS light will immediately come on since the firmware outputs a READ ON control command The DATA light however will remain off until program data is detected on the tape at which time it will begin to flicker When it stops flickering it means that the program data has been loaded to the computer s memory but don t forget that the program counter data was also written to the tape so the next flicker is that of the program counter being loaded A S9 was also written to the tape which is an end of tape marker Upon reading this the computer will output a READ OFF control command forcing the read STATUS light to go out hence ignoring all subsequent data Stored on the tape should the recorder be left to run The program as well as the program counter have been loaded Simply typing in the character G for go should initiate the program MIKBUG is a registered trademark of Motorola Inc 15 Interfacing to a SWIPC 6800 and non CT 1024 300 Baud Terminal System The terminal used must be a 300 baud RS 232 terminal
9. was not written to tape a will not be printed and the read STATUS light will have to be manually reset OFF immediatel ly upon loading th e second string of data 59 is then manually typed in from the terminal s keyboard and the computer responds with a The program as well as the program counter have now been loaded Simply typing in the character G for go should initiate the program 17 Interfacing to a SWTPC 6800 and non 300 Baud Terminal System Since the AC 30 Audio Cassette Interface must be operated RS 232 serial at 300 baud it cannot be implemented serially between the computer s control interface and the terminal system on non 300 baud or non RS 232 terminal systems The only option the user has in these cases is to operate the AC 30 Cassette Interface thru an optional serial type interface connected to one of the unused I 0 slots on the computer system The big disadvantage here is that the MIKBUG resident tape load and dump routines are only functional on the I O slot 1 the MP C Control Interface position Locating the AC 30 Cassette Interface at any other I 0 position means that all tape load and dump routines will have to be keyed in manually by the user before the AC 30 Audio Cassette Interface can actually be used to load programs The other problem is that we no longer have any way of deriving motor control for the cassette unit since motor control commands sent out thru the MP C Control
10. Assembly Instructions AC 30 Audio Cassette Interface Introduction Cassette tape is one of the most flexible and least expensive means of mass data storage for computer systems When compared to paper tape readers and punches you ll find that although the paper tape readers can be made rather inexpensively the punches cannot Paper tape systems are typically slower and the punched tapes cannot of course be repunched and used over and over again as you can with cassettes Disk systems on the other hand offer significant advantages over cassettes but are still too expensive for many applications and for most hobbyists Even those lucky enough to have a disk system still need a more universal medium for exchanging programs Although there are several commercial digital cassette tape decks on the market today recording techniques vary and they are of course much more expensive than the average audio cassette unit As could be expected most hobbyist computer system mass data storage designs have been based on the audio cassette recorder The use of inconsistent recording techniques among the various manufacturers makes it impossible for example to record a program or data tape on a SWTPC 6800 Computer System and play it back on a MITS 680 Computer System In order to coordinate manufacturer design efforts and exploit the most effective recording technique BYTE Magazine of Peterborough New Hampshire 03458 held a symp
11. CORD RLY DRIVER Yes 52 Yes 31 9 1 27 24 ANUAL MOTOR CNTRL Yes S1 e Yes 32 d 24 READ RELAY DRIVER Yes 53 33 6 1 2 24 RELAY 2 Yes 53 Yes 34 3 24 OTOR 2A Yes 911 Yes 35 m 24 OTOR 2B Yes 211 Yes 36 50 2 24 READER ON Yes 55 Yes 37 24 RECORD Yes S4 A Yes 38 7 24 RECORD OFF Yes S4 C Yes 39 4 24 READ READY Yes D20 B Yes 40 24 RECORD READY Yes D19 B Yes 41 5 L2 24 AUDIO OUTPUT Yes S2 E Yes 42 4 24 AUDIO INPUT Yes S3 B Yes 43 LOT 24 CARRIER DELAY EN Yes 51 Yes 44 ou GROUND Yes Tl Grn Yel 45 5 18 Yes 1 Green 1 46 gm 18 VAC B Yes 1 Green 2 The complement of following MIC EAR and REMOTE Switches Indicators amp Jacks ront panel switches indicators and jacks includes the jacks for recorder A These jacks should be connected thru patch cords to times necessary to input rather than t experimentation may the cassette recorder s respective jacks It is often patch the MIC output of the cassette interface to the AUX he MIC input of the recorder to be used Some be necessary here Be sure the cassette recorder s you select have a REMOT E jack on them This is necessary in order to have cassette recorder motor control MIC EAR and REMOTE jacks for recorder B These jacks may be used for feeding a second cassette r Software packages for recorder A RECORD SELECT A B
12. D button to get to the beginning of the tape Then depress the PLAY button to advance several seconds beyond the leader on the tape Stop the recorder and this time depress the cassette recorder RECORD button Then enter a P for punch on the terminal s keyboard The record STATUS light will come on and the record DATA light will flicker as program data is stored to the cassette tape When the dump is completed both the STATUS and DATA lights will go out Do not stop the recorder instead set memory locations A002 thru A005 to dump the data stored in the program counter storage addresses as well Since the record STATUS light is not lit none of this data passing back and forth between the terminal and computer is written to the still operating recorder Again enter a P for punch The STATUS and DATA lights will again come on but only for a fraction of a second since only two memory locations are written to the tape Now while the cassette recorder is still recording flip the LOCAL REMOTE switch to the LOCAL position use the manual RECORD status switch to set the record STATUS latch and type in on the terminal s keyboard S9 Reset the RECORD status latch to the off position and stop the recorder Don t forget to flip the LOCAL REMOTE switch back to the normal REMOTE position Before trying to load this same program you might want to momentarily
13. T 1024 Terminal System Decoded Control Commands 300 Baud 16X clock RS 232 Data SWTPC 6800 CT 1024 SWTPC 6800 Computer System AC 30 NON CT 1024 300 Baud Terminal System 300 Baud 16X Clock n RS 232 Data M Editor Assembler Decode Cntrl Commands 300 Baud 16X clock if available RS 232 Data E 300 Baud 16X Clock E RS 232 Data 1 0 1 SWTPC 6800 Computer System AC 30 NON 300 Baud Terminal System Editor Assembler Decode Cntrl Commands RS 232 or TTY Data 300 Baud 16X Clock RS 232 Data 300 Baud Terminal 21 DILHWEHDS 72495 BaMOd 341135545 INS Ei Teo STA Su Jaa Vit lt SIA St MDT ST ogay 9 2 414 4 SNO 241075 Tl AS DNA OT 22 123154 5200 100 Ying 2nbueuos 4o npoureq 1 9495502 05 99 241 5 414300 oso vd 5 ove ory lt 7 aid WD 1409 23
14. alled make sure it is down firmly against the board before soldering all of its leads Be very careful to install each in its correct position Do not bend the leads on the back side of the board Doing so makes it very difficult to remove the integrated circuits should replacement ever be necessary The dot on the end of the package is used for orientation purposes and must match with that shown on the component layout drawing for each of the IC s Working from the side of the circuit board fill all of the feed thru s with molten solder The feed thru s are those unused holes on the board whose internal plating connects the TOP and BOTTOM circuit connections Filling these feed thru s with molten solder guarantees the integrity of the connections and increases the current handling capability Now that most of the components have been installed on the board double check to make sure all have been installed correctly in their proper location Check very carefully to make sure that all connections have been soldered It is very easy to miss some connections when soldering which can really cause some hard to find problems later during check out Also look for solder bridges and cold solder joints which are another common problem Since the circuit board now contains CMOS devices it is susceptible to damage from severe static electrical sources One should avoid handling
15. ape operation You will of course have to manually start and stop the recorders but no Special recording considerations are necessary which usually allows use of unmodified computer resident tape load and dump routines for program storing and loading 13 Interfacing to SWTPC 6800 and CT 1024 Terminal System As mentioned earlier the ideal configuration for using the 30 Audio Cassette Interface is with the SWTPC 6800 Computer System and CT 1024 Terminal System The Terminal system must be outfitted with the CT S Serial Interface along with the CT SO optional baud rate kit For those not already having the baud option we now offer the optional baud rate kit for 14 75 PPd in the U S The terminal and computer must be operated at 300 baud The terminal system must also be outfitted with the Computer Controlled Cursor Option This board is necessary to generate the decoded control commands which are fed to the 30 Cassette Interfac Electrically the AC 30 Cassette Interface is plugged in series between th 6800 and the CT 1024 You simply remove the plug connecting the CT 1024 Terminal System to the computer s control interface and plug it into the 30 instead A separate connector then connects the AC 30 Cassette Interface to the MP C Control Interface on the Computer System The computer s MP C Control Interface must be jumpered for 300 baud operation In this configuration all data pas
16. as is the CT 1024 Terminal System It is desirable that the terminal have an accessible 16X baud rate clock If not it is still usable but you will not be guaranteed of reliable tape reads when reading tapes in the LOCAL mode You will also not be able to record tapes directly from the terminal in the LOCAL mode since the AC 30 logic requires the terminal s 16X baud rate clock for recording If your terminal does not have control character decode circuitry you may still load programs but without software control The Editor Assembler software package requires motor control and for this reason has motor control logic fed out of unused lines on the MP C Control Interface board This means that you can derive the cassette logic control for the AC 30 Cassette Interface from a connector installed on the MP C Control Interface board This cassette control logic is only functional when the Editor Assembler Software is resident and will not operate with the MIKBUG firmware or other software packages unless the appropriate driving software has been written into them Since MIKBUGR is tolerant of non program data encountered when loading tapes we may fortunately still load and store programs without cassette logic control If by chance your terminal does have control character decode circuitry it is unlikely its timing and phasing are the same as that of the CT CA board on the CT 1024 Terminal System The Reader ON Reader OFF Record ON an Record OFF control lines
17. at the beginning of each incrementally recorded record as the 14 Editor Assembler programs do Header characters have not been used in the diagnostics so that the user may see all non control character data written to tape Some experimentation with volume control settings will probably be necessary Run the diagnostics at various volume control settings and choose the one that gives you the most reliable results Let s assume now we have a SWTPC 6800 Computer and CT 1024 Terminal System interfaced together with 300 baud RS 232 serial interfaces As mentioned earlier for this configuration the cassette interface is connected in series between th two taking full advantage of the computer s firmware resident tape dump and load routines Let s assume we have a program we wish to dump to tape which is already stored in the computer s memory with the computer s pro gram counter storage addresses A048 and A049 set to the starting location of the program Now use the memory change function to set the starting and ending addresses of the memory segment to be dumped in locations A002 thru A005 The cassette interface s switches should be set for manual motor control with the RECORD READ status switches in the center position and the LOCAL REMOTE switch in the REMOTE position Load a blank or previously erased tape into the selected cassette recorder and depress the REWIN
18. cassette interfac corder often required when using Editor Assembler Their functional description is identical to that provided When this two position switch is in the A position the will output all record data to cassette recorder A When in the B position i EAD SELECT A B Wh assette interfac t will output all record data to cassette recorder B en this two position switch is in the A position the will input all read data from cassette recorder A When in ECORD STATUS ON OF ill input all read data from cassette recorder B F This three position switch is normally left in the enter position all he state of the re OFF position will m switch in either th control entirely A switch always shows cassette interfac dependent upon the detail later R the position it w R e t READ STATUS ON OFF position allowing c state of the read 1 position will manua Switch in either th control entirely A Switch always shows cassette interfac upon the setting of later RECORD DATA INDICAT owing computer program generated control commands to set cord latch Momentarily flipping the switch to the ON or anually update the status of the record latch Leaving the e ON or OFF position will override computer program convenient LED status indicator just to the left of this the state of the record latch The operation of the as a fun
19. cassette interface s control panel The PC board in turn is mounted inside a 12 3 4 wide X 3 high X 11 deep aluminum chassis with dress panel and perforated cover PC Board Assembly NOTE Since all of the holes on the PC board have been plated thru it is only necessary to solder the components from the bottom side of the board The plating provides the electrical connection from the BOTTOM to the TOP foil of each hole Unless otherwise noted it is important that none of the connections be soldered until all of the components of each group have been installed on the board This makes it much easier to interchange components if a mistake is made during assembly Be sure to use a low wattage iron not a gun with a small tip Do not use acid core solder or any type of paste flux We will not guarantee or repair any kit on which either product has been used Use only the solder supplied with the kit or a 60 40 alloy resin core equivalent Remember all of the connections are soldered on the bottom side of the board only The plated thru holes provide the electrical connection to the top foil Before installing any parts on the circuit board check both sides of the board over carefully for incomplete etching and foil bridges or breaks It is unlikely that you will find any but should there be on specially on the TOP side of the board it will be very hard to locate and correct afte
20. citor mfd 10 VDC tantalum capacitor 00 mfd 25 VDC electrolytic capacitor 1 mfd disc capacitor Semiconductors 40 40 40 45 40 40 40 59 14 4 78 1N 4 7 1 Ta 2N 2N 13 dual D flip flop 01 quad NOR gate 70 quad EX OR gate 58 dual op amp 53 triple multiplexer 49 hex buffer 23 triple 3 input NAND gate 5 timer 89 quad RS 232 receiver 88 quad RS 232 transmitter 05 5 VDC regulator 4148 silicon diode 7 volt zener diode 1N4732 or IN5230 5 volt zener diode 1N4737 or 1N5236 4003 silicon rectifier ght emitting diode 5210 NPN transistor 5087 PNP transistor RLY1 RLY2 51 53 54 SS 56 57 1 1 Misc 6 VDC reed relay DPDT miniature toggle switch SPDT center off miniature toggle switch SPDT miniature toggle switch 18 VAC 300 Ma secondary 120 240 VAC 50 60 Hz primary power transformer 1 amp standard fuse Chassis Assembly Sandwich the dress panel between the chassis and mounting hardware and attach switches 51 57 to the chassis using the wiring pictorial to show proper location and orientation Secure each switch using a finishing washer and nut Insert each of the four LED plastic mounting clips into the front panel holes provided for LED diodes D19 thru D22 Insert each of the LED diodes into the clips so that the flat on the side of each diode matches with that shown in the wiring pictorial Just for reference the side wit
21. ction of the state of the record latch is setting of the motor control switch which is described in This three position switch is normally left in the center omputer program generated control commands to set the atch Momentarily flipping the switch to the ON or OFF lly update the status of the read latch Leaving the e ON or OFF position will override computer program convenient LED status indicator just to the left of the the state of the read latch The operation of the as a function of the state of the read latch is dependent the motor control switch which is described in detail OR This LED indicator shows the transmission of valid record data out of latch is on and log operator to confirm data marking output the cassette interface It lights only when the record ic zeros or spaces are being transmitted This allows the that a tape dump is in progress when lit since the null does not light the indicator 10 EAD DATA INDICATOR This LI nto the cassette interfac light the indicator R ED indicator shows the receipt of valid read data 1 It lights only when the read latch is on valid FSK data is detected on the tape and logic zeros or spaces are being r eceived This allows the operator to confirm that a tape load is in progress hen lit since the null data marking input or a loss of audio tones does not MOTOR CONTROL MANUAL AUTO The position of the motor control
22. e inhibits all read recorder data until valid audio tones are etected at which time all incoming cassette data is stored to the computer read recorder s motor is started ncremental tapes have blank gaps betw nterface s audio tone sensing circuitry has been designed to ignore all but he valid data segments stored on the tape nd simultaneously displayed on the terminal only if the computer s echo is 11 T d a enabled Reads may be either continuous or incremental start stop Since i n recorded segments the cassette i t LOCAL REMOTE switch The LOCAL REMOTE switch on this cassette interface is analogous to that on standard teletypewriters In the LOCAL mode there is a direct data link between the terminal and cassette recorder s The computer is electrically eliminated from the system In the REMOTE or normal mode of operation the computer terminal and cassette recorder s are all linked together POWER ON OFF This switch controls AC power to the cassette interface unit It must be powered up consistently with the interconnected computer and terminal systems even if cassette operation is not desired Attaching the Interface to the Recorders If you will be using the interface just for loading and storing programs and data files to and from tape you will probably need just one cassette recorder If however you will be doin
23. e wires with the wire ties supplied with the kit Snap the PC board into place WIRE FROM TO STEP LENGTH GAUGE PART TERMINAL SOLDER PART TERMINAL SOLDER 1 p ES 1 White Fl A No 2 1 Black F1 A Yes 3 E Tl Blk White 56 No 4 PI Red Blk 56 Yes 5 line F1 B Yes cord 6 line 56 Yes cord 7 9 24 S1 B No 55 No 8 d 24 S1 E No J6 B Yes 9 T27 24 S1 E No S7 B Yes 10 4 24 52 Yes J6 A Yes T 3 24 52 Yes J7 A Yes 12 2 24 52 Yes 53 D No 13 24 24 S2 C Yes S3 14 2 172 24 S3 A Yes J9 A Yes 15 3 1 27 24 S3 C Yes J8 A Yes 16 2 24 53 Yes S5 B Yes 17 2 24 S4 B No D20 A No 18 T 72 24 S5 A No D19 A Yes 19 24 D20 A Yes D22 A No 20 T 1 27 24 D22 A Yes D21 A Yes 21 pt 24 OTOR 1A Yes J10 B Yes 22 5 1 2 24 5 Yes 51 Yes 23 92 24 READ DATA Yes D22 B Yes 24 57 24 GROUND Yes 51 Yes 25 6 1 2 24 RELAY 1 Yes 53 Yes 26 24 RECORD DATA Yes D21 B Yes 27 4 1 2 24 OTOR 1B Yes J10 A Yes 28 Tar 24 OCAL REMOTE Yes 57 Yes 29 Ad 24 READER OFF Yes 55 30 8 24 RE
24. ell as other in terconnections to the unit should be installed just as it is shown in the inter connection drawing for the SWTPC 6800 and CT 1024 Terminal System Let s assume now that we have a SWTPC 6800 Computer System AC 30 Cassette Interface and 300 baud terminal system and are taking cassette control commands off the MP C Control Interface on the SWTPC 6800 Computer System Although the AC 30 Cassette Interface is in series between the computer and terminal systems we have no means of getting the cassette control commands to the cassette interface sinc t a he MIKBUG R firmware does not generate cassette control commands on the MP C ontrol Interface board Once the Editor Assembler program has been loaded the nput output routines within the package provide the necessary cassette control commands required for the software motor control mode of operation of the package 16 You do not have to have cassette control logic to simply load and store programs with the AC 30 Cass tte Interface alt hough it is easier to use if you do Let s assume now we have a program we wish to dump to tape which is already stored in the computer s memory with the computer s program counter storage ad dresses A048 and A049 set to the s memory change function to set the starting and ending addresses of the memory segment to be dumped in locations A002 thru A005 The cassette interface s switches
25. f a sinusoidal audio waveform which is more easily handled by audio recorders Incoming audio data is first fed into a high pass filter consisting of R5 and C5 and then onto comparator IC4B The comparator s 0 5 volt hysteresis reduces th possibility of false triggering The 7 5 volt zener regulated power busses feeding ICA are necessary to stabilize this hysteresis value Zener diode clamp D3 limits comparator IC4B s output to CMOS compatible voltage levels Each time the comparator changes states IC3C and IC3D generate a 5 microsecond negative pulse at IC3 pin 11 This pulse is repetitive when data is being received and pulls capacitor C7 down to ground thru diode D4 Capacitor C7 s output is in turn inverted and buffered thru IC3A to form the CARRIER DETECT output signal This same negative going pulse is inverted by IC2A where it feeds four separate circuits The first is a missing pulse detector composed of transistor Q2 and inverter IC2B This forces the buffered CARRIER DETECT signal low whenever several cycles of audio carrier are missed The second circuit is also an adjustable missing pulse detector but this one times out whenever 1200 Hz or space data is being fed into the demodulator Trimmer resistor R16 sets the period for this timer The third circuit driven by this pulse is flip flop ICIA which outputs the demodulated data This DATA OUT line is high when 1200 Hz audio is being demodulated and low when 2400 Hz audio i
26. g tape file editing or using assembler packages you will probably have to use two cassette recorders The same single interface will handle both configurations Electrical connections between the cassette interface and recorders are best made by cutting several 3 to 4 audio patch cords with the molded RCA connectors on both ends in half and fitting the newly cut ends with the appropriate recorder jack mating connectors Some cassette recorders such as the ones used with the prototype have both high level AUX and low level MIC inputs In our case it was necessary to use the AUX input since the cassette recorder circuitry would not permit the reading of a tape with a plug simultaneously installed in the MIC jack Be sure to use a cassette recorder featuring an AGC automatic gain control circuit Most all late model cassette recorders have this 5 eature Since cassette motor control is available you will want a recorder with EMOTE jack that stops the recorder s motor Here again recorder circuitry varies ome units disable just the motor while others disable everything It is best in this instance to just disable the motor the idea being to minimize the recorded transients between blocks of data when using the interface in the incremental start stop mode of recording The recorders used with the prototype were Superscope models C 101A Although they were reliable close examination of the quality of
27. h the flat is the same as the side with the shorter lead Secur ach LED diode with the plastic retaining ring This ring must be pressed on tightly to prevent the LED from being loose Attach RCA jacks J6 thru J9 to the chassis Jack J6 should have a ground lug put under it Secure each jack with a 1 4 nut RCA jacks J10 and 711 must be electrically insulated from the chassis In order to do this first slip a shoulder washer over each RCA jack with the shoulder against the inside of the chassis place the jack against the outside of the chassis put another shoulder washer on the back side of the jack with the shoulder against the inside of the chassis follow this with the ground lug and finally secure with a 1 4 nut Attach the power transformer to the chassis using 6 32 X 1 4 screws lockwashers and nuts Orient the transformer so the end with the three wires coming out of it is toward the front of the chassis Attach the fuseholder to the chassis using a 6 32 X 3 8 screw lockwasher and nut Snap the four nylon PC board supports into the holes provided for them in the chassis Snap the 1 1 2 bushing into the large hole provided on the back of the chassis The bushing should be installed from the outside of the chassis Turn the chassis upside down and attach each of the four press on rubber feet about 1 in from each of the corners Using a pair of pliers crimp the strain relief ont
28. m your terminal to the AC 30 Cassette Interface otherwis n the terminal and computer is written to ill again come on but only for a fraction of omit this step N flip the LOCAL REMOTE switch back to record STATUS light OFF ow you may stop the recorder Don t forget to the normal REMOTE position and reset the Before trying to load this same program you might want to momentarily turn the computer off just to make sure th loading Reapplying power will force R firmware on the SWTPC 6800 Rewind cassette recorder s volume is set to button Then type in a L for load on light ON The DATA at which time it wil ight will remain l begin to flicke memory resident program is destroyed befor an auto reset and bring up the resident MIKBUG the tape to the beginning Make sure the a reliable setting and depress the play the terminal s keyboard set the read STATUS off until program data is detected on the tape r When it stops flickering it means that the program data has been loaded to the computer s memory but don t forget that the program counter data was also written the program counter tape marker a wil being loaded If 1 be printed on t to the tape so the next flicker is that of an S9 was written to tape which is an end of he screen upon termination of loading The read STATUS light must be immediately manually reset OUT If an S9
29. mmunication with the computer system If you flip the same switch to the LOCAL position you should find that everything typed on the terminal s keyboard is echoed to the terminal s screen even though the ECHO ON OFF switch on the keyboard is in the OFF position Before you actually try to load or store a program on tape the unit must be calibrated using the FIVPNT 1 Interface Calibration Program A copy of this program is contained within a separate section of this instruction set It might also be wise to run the other diagnostic programs which are also contained within this instruction set When you are running the diagnostic programs you may find that the terminal will occasionally omit a character when reading a tape back in the LOCAL mode This as we found is a problem in the terminal and not in the AC 30 Cassette Interface If you wish to correct the problem carefully separate pin of IC31 on the CT 1024 Terminal System from its connection to the circuit board Attach and solder a wire from this now isolated pin to IC26 pin 13 It is a good idea to increase the value of C4 on the CT CA board on the CT 1024 Terminal System from 100 capacitor to a 1000 pfd capacitor You may also find when you are reading back tapes recorded in the incremental mode that question marks occasionally show up between incrementally recorded records This is where the AC 30 is most vulnerable to errored reads and is best solved by your putting a header character s
30. ncorrectly 522 Install the transistors nsert the small nylon indexing plugs rows on the into the edge connector pins indicated BOTTOM side of the circuit board his prevents mating plugs from being accidentally plugged onto the board the board The transistors must be turned to match the outlines on the component layout drawing Solder Install all of the diodes on the board excluding diodes D18 thru D22 The diodes must be turned to match the outlines on the component layout drawing Solder Install LED diode D18 on the circuit board Be sure the flat on the side of the LED matches that shown on the component layout drawing Attach the diode is 1 8 to 1 4 above the top of the board Solder so the bottom of its case Install reed relays RLY1 and RLY2 on the circuit board These relays not polarized so they need not be oriented in any particular position other than matching the end with three leads and the one with just one to the respective holes on the circuit board Solder Install integrated circuit IC16 on the circuit board This component must be oriented so its metal face is facing the circuit board The IC is secured to 4 40 X 1 4 screw lockwasher and nut The three leads of the integrated circuit must be bent down into each of their respective holes and trimmed Solder the circuit board with a NOTE Most of the integrated circuit
31. o the line cord at a point 12 from the end of the cord While compressing the strain relief insert th 12 length of the line cord and the strain relief into the 7 16 hole provided on the back of the chassis from the outside of the chassis Press the specified color of switch cap onto the handle of each toggle switch as specified below 1 white 2 green S3 green 54 yellow 55 yellow S6 red S7 white Snap the ten tinnerman clips onto the holes provided on the front and back lips of the chassis Chassis Wiring All connections made between the components on the chassis and the printed circuit board are made thru connectors 21 J2 This allows one to easily remove the PC board for service or access to the bottom side of the PC board When soldering the wires to the main plugs for connectors 21 J2 the plugs must not be plugged into the PC board If they are the femal connectors may melt and be ruined Follow the wiring steps outlined on the next two pages Note for 220 VAC Operation To wire the unit for 220 VAC operation omit wiring steps 1 thru 4 and instead solder together and insulate 1 5 BlackWhite and Black leads Then connect Tl s White wire to Fl terminal A and solder Also connect 1 5 Red Black wire to 56 terminal and solder Plug connectors 21 and J2 to the appropriate jacks on the PC board Be sure to orient the jacks correctly Bundle any loos
32. oftware problem than a hardware problem and thus a little easier to resolve Although the SWTPC AC 30 Audio Cassette Interface has been used extensively with the SWTPC 6800 Computer System and CT 1024 TV Typewriter II Terminal System it has been designed to be as universal and flexible a system as possible If your computer s control terminal is interfaced to the computer thru 300 baud RS 232 compatible serial interfaces with accessible UART type 16 X baud rate clocks on both computer and terminal the SWTPC AC 30 Cassette Interface Unit is simply plugged between the computer and terminal interfaces This is the ideal mode of Scanned and edited by Michael Holley Feb 16 2002 Southwest Technical Products Corporation Document Circa 1976 operation since the cassette unit can take full advantage of computer resident tape load and dump routines and requires no additional interfaces Switching the cassette unit to the LOCAL mode directly interconnects the terminal and cassette unit for terminal only cassette tape operation just like the LOCAL mode of operation on teletypewriters While operating in the REMOTE mode the computer communicates with both the terminal and cassette unit here again just like the REMOTE mode of operation on teletypewriters Those customers using the CT 1024 TV ak ypewriter Terminal System or terminal system with acces
33. osium in the Fall of 1975 in Kansas City in an attempt to establish a recording standard for the storage of digital data on audio cassette recorders The standard which was adopted has been tested and fully supported by Southwest T Technical Products Corporation It appears to be the best compromise between economy and reliability Although complete details are contained in the Feb 1976 issue of BYTE Magazine the recording philosophy is to record data serially using the standard UART format at 300 baud 30 characters second Marks or logic ones are represented by recording a 2400 Hz sine wave on the tape while spaces or logic zeroes are represented by recording a 1200 Hz sine wave With the proper circuitry this recorded data can then be read off the tape and transposed into a self clocking UART based tare system which will tolerate audio recorder speed variations of approximately 30 This figure is far better than that of most other modulation techniques and is a real advantage when you consider the degr of worst case speed variation between inexpensive audio recorders In addition we have speed variations due to line voltage battery voltage wow and flutter mechanism wear etc Thus evolved the Kansas City standard It should be noted that the standard does not specify how the data is to be organized on the tape so there can and probably will be some incompatibility among various manufacturer s units This is however more of a s
34. peration for the cassette system 18 You will have to write your own cassette tape I 0 routines in order to be able to load and dump programs to and from the 30 Cassette Interface which is now interfaced to an MP C Control Interface somewhere other than 0 Card position 1 You should be able to use the MIKBUG R source listings of the tape load and punch routines to aid you in writing your own for the cassette interface If the routines are kept short enough you might be able to load them into unused areas of the MIKBUG RAM which would give your programs complete use of 0 32 user memory The tape load and dump programs will however have to be typed in manually from the terminal before using them How It Works For simplicity the cassette interface s circuitry has been broken up into thr separate systems The modulator demodulator circuitry the switching circuitry and the power supply The modulator works by feeding a 4800 Hz 16 X 300 baud clock into divide by two IC5B This insures 50 duty cycle required by the modulator The CARRIER ENABLE input provides a means of suppressing audio output from the modulator 1 5 functions as a divide by two if the DATA IN line is high and a divide by one if the DATA IN line is low This gives 1200 Hz tone for a low and a 2400 Hz tone for a high This resulting output is then fed into two pole active filter IC4A where it is converted to more o
35. position is quite different If both the record and read latches are reset thru the respective R EMOTI cassette recorder motor operation is inhibited E jacks on both the record and read recorders The interface s selected record MIC jack will output no audio data even if there is data flowing back and forth between the computer and terminal As soon as the record latch is turned ON thru the respective R EMOTI E jack and a variabl e del the recording recorder s motor is turned on ay timer is fired which delays the output of audio marking data to al recorder s tape to come up to normal tape speed llow this same cassette This hardware delay circuit must be supplemented with a software delay loop written into your programs to guarantee that you don t start outputting record data until after this hardware delay timer on the cassette interfac the record latch is again turned off has already timed out When the interface will cease to output audio data and the selected recorder s motor is turned off Here again it is wise to include a software delay time to come to a complete stop loop in your programs to give the recorder This guarantees a sufficient gap between multiple recorded segments to allow one to do either incremental start stop or continuous reads from the same tape When the read latch is turned on th he interfac
36. r all of the components have been installed on the board Attach all of the resistors to the board As with all other components unless noted use the parts list and component layout drawing to locate each part and install from the TOP side of the board bending the leads along the BOTTOM side of the board and trimming so that 1 16 to 1 8 of wire remains Solder You may find that there are no pads on the BOTTOM side of If not be sure its two leads are soldered from the board for resistor R42 the TOP side of the boar d Install all of the capacitors on the board Be sure to orient the electrolytic capacitors co layout drawing The body o Solder gt 5 Starting from one end of t femal dge connectors alo inserted from the TOP si gainst the board Make su ircuit board rrectly The polarity is indicated on the component f electrolytic capacitor C21 should be insulated so as not to short to foil conductors under it If the body of the capacitor is not insulated attach the capacitor so it is up off the board about 1 8 he circuit board install each of the five Molex ng the edges of the board These connectors must be de of the board and must be pressed down firmly re the body of the connector seats firmly against a the circuit board and that each pin extends completely into the holes on the by the small triangular ar T i
37. recorded data with an oscilloscope left a lot to be desired The optimum volume control setting was around 7 on a scale of 0 to 10 The quality of the cassette tape used with your recorder s will also affect the reliability of your system Here the best rule of thumb is to assume you get what you pay for The most expensive tapes will generally give you better reliability Remember too that you are recording audio frequency data not saturated pulses so don t use digital computer grade cassette tapes Always erase previously recorded tapes with a bulk tape eraser such as a Radio Shack 444 210 9 95 before rerecording them This is especially important when using the system in the incremental start stop mode of operation Bulk tap rasers generally do a better job of erasing than your recorder s internal circuitry and guarantee that you don t pick up segments of previously recorded programs or data Superscope is a registered trademark of Superscope Inc 12 The interface s read circuitry must be calibrated for use in the read mode before using the interface This is best done by using your computer or terminal to generate a calibration tape with continuous ASCII 5 s recorded on it and then reading back the tape to the computer in the REMOTE mode or terminal in the LOCAL mode while adjusting trimmer resistor R16 for a center setting between errored reads ASCII fives have an alte
38. rnating bit sequence ideal for calibration It is a good idea to periodically recheck this setting using your previously generated calibration tape Before using your cassette interface unit in the incremental start stop mode of recording it will be necessary to set the time delay on the carrier enable one shot trimmer resistor R39 so as to allow the recorder s motors to come up to Speed before outputting a marking audio tone This is best done by visually measuring your recorder s motor start time and then multiplying by two just for a safety factor The interface s delay is then set by adjusting trimmer resistor R39 for this same time delay between the time the RECORD READY indicator lights and the CARRIER ENABLED indicator LED diode D18 comes on The latter is mounted right on the interface s PC board adjacent trimmer resistor R39 Whenever you are writing to tape in the incremental start stop mode you must provide a software delay loop in your program that is at least as long as the adjustable hardware timer delay plus 0 5 seconds The additional half second is required to guarantee a carrier detect signal before data flow when the tape is being read It is also a good idea to put a header character or characters at the beginning of each incremental record Upon reading these records your program should be written such that it ignores all data between these recorded segments until
39. s being demodulated The fourth circuit fed by the pulse is IC2D which with the addition of the output of IC3B synthesizes the 16 X CLOCK OUT data Take note that although this 16 X clock is accurate it by design jitters Within the switching portion of the circuit integrated circuit halves IC8A and IC8B form RS status latches for the record and read circuitry Either latch may be independently set or reset thru manual toggle switches on the interface s front panel or thru control pulses buffered and selectively inverted by IC13 Convenient front panel LED indicators always show the current status of these latches 19 The multitude of data and clock switching is performed by six data selectors within IC6 4 NAND gates IC9A and IC9B inhibit data and clock flow out to the cassette recorders unless the read latch is set and valid recorder carrier data is detected Timer IC10 provides the adjustable CARRIER ENABLE delay needed when using the system for recording in the incremental start stop mode All 300 baud data communication with the cassette interface is done thru integrated EIA RS 232 receiver and transmitter integrated circuits IC12 and IC15 respectively Motor control for each recorder is provided by reed relays RLY1 and RLY2 20 INTERCONNECTION BLOCK DIAGRAMS SWTPC 6800 Computer System 30 C
40. s used in this kit are CMOS and are susceptible to damage by static electricity Although some degree of protection is provided internally within the integrated circuits their sensitivity demands the utmost in care Before opening a should ground your body and all nd or install ling any CMOS integrated circuits you metallic tool S coming into contact with the leads thrua 1 M ohm 1 4 watt resistor earth ground such as a water p supplied with the kit The ground must be an ipe and not 3 the circuit board ground As for the connection to your body attach a clip lead to your watch or metal ID bracelet Make absolutely sure you have the 1 Meg ohm resistor connected between you and the earth ground otherwise you will be creating a dangerous shock hazard Avoid touching the leads of the integrated circuits any more than necessary when installing them even if you are grounded On those MOS IC s being soldered in place the tip of the soldering iron should be grounded as well separately from your body ground either with or without a 1 Meg ohm resistor Most soldering irons having a three prong line cord plug already have a grounded tip Static electricity should be an important consideration in cold dry environments It is less of a problem when it is warm and humid Install integrated circuits ICI thru IC15 following the precautions given in the preceding section As each is inst
41. sible control haracter decoders may even pick Reader ON Control Q Reader OFF Control S Record On Control R and Record OFF Control T control commands right off the control character decoder circuitry on their terminal system giving the computer system program control over cassette recorder data flow and even motor operation Those not having access to decoded control commands may still have cassette control by driving the cassette interface with control lines from a separate parallel interface option located on the attached computer system Those users not operating their control terminal RS 232 serial at 300 baud or not having access to their terminal s 16 X UART clock may still use the cassett interface but must attach it to the computer system thru a separate RS 232 serial 300 baud interface with accessible 16 X clocks located on the computer system This however eliminates the ability to use the computer resident control terminal tape load and dump routines as well as the LOCAL REMOTE feature described previously The cassette interface circuitry is constructed on a 7 3 4 X 7 1 2 double sided plated thru hole fiberglass circuit board with all electrical connections made to the board thru one of the fiv dge connectors The thr connectors along the back edge of the circuit board are for connections to the computer control decoder and terminal while the two along the front edge are for connections to the
42. sing between the computer and terminal may if selected be written to tape or supplemented with data from tape Connections from the 1024 Terminal System s CT S Serial Interface 16 baud rate clock Computer Controlled Cursor decoded control command logic are made to the AC 30 Cassette Interface thru the center connector on the back of the AC 30 circuit board The SWTPC 6800 CT 1024 Interconnection Drawing shows all connections that need be made for this configuration The AC 30 Cassette Interface must always be powered up when using the system even if you are not using a cassette tape sinc all computer terminal data flow is thru the cassette interface After attaching the supplied connector to the CT 1024 Terminal System you should note that the 16 clock for the CT S Serial Interface was broken when installing the cassette connector This brake prevents the CT 1024 Terminal System from operating if it is not attached to the AC 30 Cassette Interface For this reason the connections for a dummy plug have been shown which must be plugged onto the CT 1024 Terminal System s connector for stand alone operation so don t forget to install the dummy plug on the terminal s connector when using the terminal system without the AC 30 Cassette Interface After actually interconnecting the AC 30 with your system flip the LOCAL REMOTE switch to the REMOTE position and you should find that you have normal co
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