The User Manual
Contents
1. Some adjustment may be needed for some systems Chapter 10 Code with a Halt Instruction The PIC controls the Z80 by feeding it opcodes When the Z80 executes a Halt instruction it stops fetching opcodes and waits for an interrupt or reset Some code may normally sit in a halted state waiting for an interrupt then perform some action such as checking for a key press serial character received etc then after any required tasks have been performed execute a halt and wait for the next interrupt The ICE will not work properly when executing this type of code as the Z80 stops fetching instuctions when halted and cannot be controlled by the PIC The ICE can still be used in this type of system but the code containing the Halt instruction cannot be executed To avoid executing the Halt instruction as soon as the system is powered up disable autorun mode so that the Z80 will come up paused after reset To do this reset the system hit lt Enter gt to get the sign on message and prompt then type DA lt Enter gt This will disable autorun mode This setting is saved in EEPROM Now reset the system and hit lt Enter gt to get the sign on message and prompt Now you should be able to use the ICE to test memory access I O ports etc but don t execute the code that includes the Halt instruction as the ICE won t work after that Chapter 11 Differences between this unit and Nicolet s NICE New commands not present in N2. scope loops Read Intel Hex file into memory Substitute into memory Soft reset Trace Untrace Verify Write Intel Hex file from memory Examine change registers CS Checksum memory region Adds memory contents from start address to end address inclusive and displays 16 bit sum This is a simple 8 bit accumulation with carry so the result can be more than 8 bits Only the low 16 bits of the result are displayed This should match the checksum generated by many EPROM programmers Format CS startend Addresses entered as 1 4 hex digits Format CS Example OK gt CS 0000 03FF Checksum 0x73FD D Display memory Displays memory contents from start address to end Start address is truncated so that display always starts at nnnO Multiples of 16 bytes are displayed until end address is reached or passed ASCII equivalents for the data are also displayed A dash is inserted after the first 8 bytes Format D start end Addresses entered as 1 4 hex digits Both parameters are optional If no end address is entered 0x80 bytes are displayed If no start address is entered display begins at the next address after the end of the last D or L command This is the saved memory address So entering just D will start displaying from the end of the previous D command Example ASCII section is not correct OK gt D 0002 0019 0000 C3 Fl A5 26 72 89 CE 27 F3 06 82 01 CD 00 77 BC This text do 0010
3. Format MT start end O Output to I O port Write 8 bit data entered to selected Z80 I O port Format O port d8 8 bit I O port number address entered as 1 2 hex digits P Put write data into a target system memory location Write 8 bit data entered to selected Z80 memory location This command writes to a single memory location and is useful for creating a repeated memory write operation with the Z and RL commands so that target system signals can be examined with a non storage oscilloscope Format P address d8 16 bit memory address entered as 1 4 hex digits R Read Intel Hex file into memory Used to load target system memory with test programs etc saved in Intel Hex format An optional 16 bit offset may be entered This offset will be added to the addresses in the Hex file before storing the file data in memory This is useful if the code being loaded is relocatable If no offset is entered an offset of 0 is used No offset The R command can process data and store it in the target system s memory at up to 19 2 K baud if the target system is running at 1 MHz or higher If a slower Z80 clock is used higher baud rates can cause a data overrun condition which will cause an error message to be displayed Using hardware handshake won t fix this as the PC takes too long to react to CTS going inactive In this case simply switch to a slower baud rate Format R d16 S Substitute into memory Used t
4. gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR vuy EB Enable bus requests Enables bus requests to reach the Z80 when in Go mode If this command is entered while the CPU is in Go mode bus requests will be enabled immediately A B appears on the last line of the status display if bus requests are currently enabled Bus requests are always disabled in Quit mode even if a B is displayed Format EB DB Disable bus requests Disables bus requests from reaching Z80 when in Go mode If this command is entered while the CPU is in Go mode bus requests will be disabled immediately Format DB Example OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR vvdV OK gt DB OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E IN R uvu OK gt EB OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR vuy ER Enable refresh Enables refresh bursts to occur when the Z80 is in Quit mode This setting has no effect on Go mode operation An R appears on the last line of the status display if refresh is currently enabled Format ER DR Disable refresh Disables refresh bursts when the Z80 is in Quit mode Format DR Example OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR uvu OK gt DR OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INB
5. 33 E gt 0654 66 E gt 0982 99 D INBR EPP Enable printpoint s Enables one of the three printpoints which are used by the trace and untrace commands If no parameter is entered all three printpoints will be enabled Printpoints cause the current Z80 register values to be displayed when reached and enabled during an untrace command They are compared to the current PC after each instruction is executed Note that printpoints and breakpoints share the same three address values so a particular address can be enabled as a breakpoint a printpoint or both Breakpoint pass count values don t affect printpoint operation Format EPP n nis 1 2 or 3 DPP Disable printpoint s Disables one of the three printpoints which are used by the trace and untrace commands If no parameter is entered all three printpoints will be disabled Format DPP n nis 1 2 or 3 Example OK gt EPP OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR uuv OK gt DPP 2 OK gt DPP 3 OK gt ST gt 0123 33 E P gt 0654 66 gt 0982 99 INBR moO EI Enable maskable interrupts Enables maskable interrupts to reach the Z80 when in Go mode If this command is entered while the CPU is in Go mode interrupts will be enabled immediately An T appears on the last line of the status display if maskable interrupts are currently enabled All interrupts are always disa
6. O ports etc The Trace and Untrace commands can be used in Quit mode to execute code but not at full speed Since the Trace mode displays all of the registers after each instruction its speed is affected by the baud rate being used This command is always slower than Untrace The Untrace command does not display anything after each instruction but it does grab the current PC value from the Z80 to check against breakpoints and printpoints This takes some time Also refresh adds some delay if enabled With refresh enabled and the Z80 clocked at 4 MHz Untrace executes roughly 1600 instructions second This is not fast enough to keep up with data coming off of a floppy disk so don t try to boot from a floppy in untrace mode Interrupts The ICE can recognize interrupts in Go mode but not in Quit mode In Go mode the user can enable or disable maskable or non maskable interrupts reaching the CPU Separate control of each is available In Quit mode no interrupts can reach the CPU Bus Requests The ICE can recognize bus requests in Go mode but not in Quit mode In Go mode the user can enable or disable bus requests reaching the CPU In Quit mode no bus requests can reach the CPU Memory Refresh When the ICE is in Quit mode the Z80 executes bursts of NOP instructions to provide for refresh of any DRAM present in the target system This takes up about 25 of the processor s time so if you know that your system doesn t use DRAM
7. above the CPU registers and can be used to trace backwards from the current PC value to see what the recent sequence of calls or branches was before we stoppped A maximum of 12 of these instructions will be displayed If fewer than 12 were executed during the current untrace command only that number will be displayed Format U d16 V Verify compare memory This command will verify compare two regions of memory and display any differences found Differences will be displayed as address in first region value in first region value in second region Format V start end dest Parameters are d16 All bytes from start to end inclusive will be compared W Write memory out as Intel Hex file Used to save target system EPROM images etc in Intel Hex format A 16 bit offset must be entered This offset will be added to the addresses in the Hex file before storing the file data in memory This may be useful if the code is located at an address other than 0 but you want the Intel Hex file addresses to start at 0 for loading into an EPROM programmer for instance Offset addition will wrap at 64K so OxFO000 0x1000 0x0000 If you don t want any offset just enter 0 Format W start end offset Parameters are d16 All bytes from start to end inclusive will be written Start must be a lower address than end X Examine and edit the contents of the Z80 s registers Used to display or change Z80 register contents Valid register
8. and count 1 will produce the same result Setting the count to 3 will cause a trace to stop on the third time that breakpoint matches the current PC If it is enabled If the pass count does not reach zero while a trace or untrace command is executing its value is preserved and can be examined with the ST command to see how many times that breakpoint was hit So if the pass count was set to 10 at the start of the command and is 7 after the trace or untrace stops that address was hit 3 times Format BPC n d8 nis 1 2 or 3 d8 is an 8 bit count Example OK gt ST gt 0123 00 gt 0654 00 gt 0982 00 INBR ovg OK gt BPC 1 33 OK gt BPC 2 66 OK gt BPC 3 99 OK gt ST gt 0123 33 gt 0654 66 gt 0982 99 INBR ovg EBP Enable breakpoint s Enables one of the three breakpoints which are used by the trace and untrace commands If no parameter is entered all three breakpoints will be enabled Format EBP n nis 1 2 or 3 DBP Disable breakpoint s Disables one of the three breakpoints which are used by the trace and untrace commands If no parameter is entered all three breakpoints will be disabled Format DBP n nis 1 2 or 3 Example OK gt ST gt 0123 33 gt 0654 66 gt 0982 99 INBR ovg OK gt EBP OK gt ST gt 0123 33 E gt 0654 66 E gt 0982 99 E INBR OK gt DBP 3 OK gt ST gt 0123
9. instruction so execution is much faster The registers may be displayed when specific PC values are hit using printpoints Untracing will stop if the requested number of instructions has been executed or if an enabled breakpoint has been reached A parameter must be entered to specify a number of instructions to be executed Entering U 10 will execute 10 instructions and then stop and display the registers If an enabled breakpoint is reached before 10 instructions have executed the untrace will stop immediately If the number of instructions to execute is entered as 0 the untrace instruction will continue until a breakpoint is hit and will not stop based on instruction count When the untrace command stops the total number of instructions executed during this one command is displayed This could be used to count for instance how may Z80 instructions are executed between system reset and a prompt appearing Ctl C can also be used to stop the untrace command If the Z80 encounters a Halt instruction when untracing it will stop fetching opcodes and will no longer be controllable by the ICE A message will be displayed in this case and the system will need to be reset to restore normal operation During an untrace command the Z80 s PC is monitored and when instructions that modify it such as branches calls and returns are executed their address is saved in a 12 entry FIFO buffer When the untrace command stops these instructions are displayed
10. selection arguments are F A B D H S P F A B D F X and Y HL BC and DE must be edited as a 16 bit pair Format X regsel If no register selection argument is enterred the complete register set will be displayed Example OK gt X Z V A 00 BC 1234 DE F74C HL 5542 S FFFO P 824D LD A L S C A 4C B 1A64 D F29C H 0000 X FFFO Y 824D I 00 Chapter 7 Cabling Information Two ways to connect ribbon cable depending on how you want ribbon cable to face on target system Right Angle Header Normal Connection r ICE C t DIP pl ket Components on this side A plugsacke 21 20 ae vA Ribbon Cable oo cae Red Stripe DIP Plug 1 raised pin numbers Pin 1 of 280 connects here are correct Pin 1 of ZRO connects here Reverse Connection ICE 1 40 0 Please be careful when using this connection as the pin numbers on the DIP plug and the red stripe will be Ribbon Cable misleading Plugging the ICE in incorrectly will probably damage it 20 21 ae N Red Stripe DIP Plug Right Angle Header raised pin NEA numbers Components on this side are incorrect Chapter 8 How does it work The ICE consists of a 6 MHz Z80 CPU a CPLD custom logic chip an RS 232 level translator charge pump chip and a PIC microcontroller The PIC chip communi
11. you may want to disable refresh to speed up instruction tracing In Go mode the Z80 is executing at full speed so no extra refresh provision is needed Since refreshing DRAM s requires a certain number of refresh cycles in a certain period of time if the system clock is too slow it will be impossible to meet this requirement If the Z80 s clock is below 200 KHz refresh will be disabled at start up To meet a typical DRAM refresh requirement the clock would need to be more like 2 MHz anyway Reset The PIC MCU uses the same reset signal as the Z80 so it comes up in a known state whenever the Z80 gets reset Maskable and non maskable interrupts are enabled or will be at least when Go mode is entered Bus requests are enabled as well The ICE comes up in Quit mode unless Autorun is enabled then it comes up in Go mode with the Z80 executing code All breakpoint and printpoint enables are cleared The saved memory address is set to OXFFFF More on this later The default PC starting value for the next G command is reset to 0000 Since the PIC gets reset whenever the Z80 is reset you need to send it a carriage return to allow the auto baud detection to complete If characters are not echoed to the terminal after you see the version text displayed reset or power down the target system and try again BP BPC EBP Chapter 5 Go Mode Commands These commands can be entered in either mode except Q Set breakpoint ad
12. 0000 004F FF RST 38 0050 FF RST 38 0051 FF RST 38 0052 FF RST 38 0053 FF RST 38 0054 FF RST 38 OK gt M Move memory block Moves a block of memory data from one area of memory to another The destination area must be writeable for the command to work but no attempt is made to confirm that the write actually succeeded Format M start end dest The block of data between start and end inclusive is copied to a new area of memory starting at dest MD Memory detect Reads and writes 16 bytes at start of all 64 1K pages of target memory and tries to detect read only memory and RAM If data always reads the same despite writing several patterns we assume its read only memory If data always matches what we wrote we assume it s RAM Data in each 1K page is compared with data in lower 1K pages to detect stuck or unconnected upper address bits or the same memory appearing several times in the memory space Page number displayed is lowest 1K page in target memory that contains the same data as this one If no memory repeats then each page will display its own page number Note that if the bus always floats to the same value or is terminated to a logic one level when floating the data will always read the same so it will be detected as read only memory Note Executing this command will write to the first 16 bytes of every page so memory contents will be changed Format MD Example 000000000000000011111111111111112222222
13. 1 KHz resolution Minimum displayable clock rate is 19 KHz Format CF Example OK gt CF Z80 clock frequency is 3 976 MHz Q Quit Quit stop Z80 and enter Quit mode Format Q Example Z V A 00 BC 1234 DE F74C HL 5542 S FFFO P 824D LD A L S C A 4C B 1A64 D F29C H 0000 X FFFO Y 824D I 00 RL Repeat Line This command may be used to repeat a command or group of commands on a single command line This could be used together with the sleep command to create a repetitive write to the same memory location for instance so that an oscilloscope can be used to observe timing and signal behavior To break out of the loop press Ctl C Example OK gt P 8000 A5 Z 9 RL Above command line will write 0xA5 to address 0x8000 then it will delay for 9 mSec then repeat The actual delay between writes will be longer if refresh is enabled ST Status Display breakpoint printpoint and hardware status The first three lines of the status display are devoted to breakpoint printpoint information The first value is the address which will be compared to the PC The second value is the breakpoint pass count The third value is either a D or E which indicates whether that address and pass count are currently enabled E or disabled D as a breakpoint The fourth value if displayed is a Pif the address is currently enabled as a printpoint The fourth line shows the current state of the three hardware en
14. 2222222223333333333333333 0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF RRRRRRRR RRRRRRRR RRRRRRRR 00000000 00000000 WWWWWwWww 00000000 00000000 33333333 01234567 01234567 89ABCDEF Above display shows 8K Read only memory located in first eight 1K pages and the same memory appears at 32K as well An 8K RAM appears only in the top 8K pages 0000000000000000111111111111111122222222222222223333333333333333 0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR WWWWWWWWWWWWWWW WWW WWW WWW WWW WWW WWWWWWWWWWWWWwWWwwwwwwwwwOOOOOOO0O 0000000000000000111111111111111122222222222222223333333333333333 0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF Above display shows 8K Read only memory located in top eight 1K pages The rest of the address space is filled with RAM that is fully decoded Does not repeat MT Memory test Performs a destructive test of memory by writing a rotating pattern of first a single bit then a single 0 bit and the rest ones to each memory location in the indicated range After the pattern is written to the entire area all locations are checked to see if the value read matches what was written Any mismatches are displayed as address value written value read The entire memory range is written and read 16 times so any particular address may appear in the error list up to 16 times if it fails for all data values
15. 3c 1F 5A 62 CE 98 CE 27 F3 06 82 01 CD 00 77 BC es not go with t OK gt D 0020 C3 Fl A5 26 72 89 CE 27 F3 06 82 01 CD 00 77 BC he data on the 1 0030 3C 1F 5A 62 CE 98 CE 27 F3 06 82 01 CD 00 77 BC eft 0eee 0040 C3 Fl A5 26 72 89 CE 27 F3 06 82 01 CD 00 77 BC I once shot an 0050 3C 1F 5A 62 CE 98 CE 27 F3 06 82 01 CD 00 77 BC elephant in my p 0060 C3 F1 A5 26 72 89 CE 27 F3 06 82 01 CD 00 77 BC ajamas what he 0070 3C 1F 5A 62 CE 98 CE 27 F3 06 82 01 CD 00 77 BC was doing in my 0080 C3 F1 A5 26 72 89 CE 27 F3 06 82 01 CD 00 77 BC pajamas I 11 nev 0090 3c 1F 5A 62 CE 98 CE 27 F3 06 82 01 CD 00 77 BC er know E Examine a single memory location Input 8 bit data from selected Z80 memory address and display it This command reads from a single Z80 memory location unlike the D command and is useful for creating a repeated memory read operation with the Z and RL commands so that target system signals can be examined with a non storage oscilloscope Format E address 16 bit memory address entered as 1 4 hex digits F Fill memory Fills memory from start address to end with the value given Format F start end value Addresses entered as 1 4 hex digits Value is 1 2 hex digits Same value is written to every location No attempt is made to verify that the write succeeded G Go Go Start Z80 CPU executing at full speed Format G starting address Starting address entered as 1 4 hex digits If no starting a
16. 80 chip would use the EA command to enable AutoRun mode This setting will be saved in EEPROM and the next time you power up the Z80 will start executing from address 0 after reset ends The DA command can be used to disable AutoRun mode Chapter 3 Command Line Interpreter Commands may be entered in either upper or lower case All numeric values such as addresses or counts are entered and displayed in hex When entering a 16 bit value d16 1 4 hex digits can be entered 1 or 2 digits can be entered for an 8 bit value d8 If a command accepts parameters it must be followed by a space The parameters can be separated by either a comma or a space Each command must be followed immediately by either a semicolon or a carriage return The command line can hold up to 31 characters Once that limit is reached you should hear a beep from the terminal Any additional characters entered will replace the last character on the line The command s on the command line will be executed when a carriage return is typed There are two prompts OK gt indicates the last command was accepted and executed without error ERR gt indicates that the last command was either not accepted or caused an error when it was executed In either case the ICE is ready for a new command to be entered Some commands may take a long time to execute and you may decide to abort the command The following commands may be either paused using Ctl S then resu
17. ICE CF Measure clock frequency CS form 16 bit checksum of memory block E Examine and display a single memory location for scope loops MD Try to detect RAM and EPROM in target memory space P Put data into a single memory location for scope loops W Write out memory as Intel Hex DN EN separate hardware control of NMI input EA DA control start up behavior Go or Quit display help screen with command list Other differences L command displays hex data bytes along with instructions L command resolves branch target addresses L command handles undocumented Z80 opcodes M command checks for overlap between source and destination regions and changes move order if nec U command displays branch trace instead of the last few PC values as backtrace U and T commands check for of instructions 0 which disables instruction count limit U command displays total instructions executed since start of command Z80 Halt output is monitored and a message is displayed if CPU is halted Z80 operation at much lower frequencies is supported because we measure the Z80 clock and scale our timings accordingly The NICE does not operate properly at 500 KHz and below IC sockets enable using different Z80 chips or replacing PIC or RS 232 chip if damaged RS 232 level translator chip is used to provide better voltage levels to PC or terminal NICE uses 5V and Gnd R command read Intel Hex can operate at higher baud rates The manual for
18. Z80 ICE User Manual Code Version 0 63 or V0 64 5 23 09 Chapter 1 Introduction Background The Z80 microprocessor was very popular in the late 1970 s and early 80 s and was designed into a number of computer systems It is probably still being designed into new products as a CPU core in highly integrated VLSI chips for consumer products Other CPU s from this era such as the 6502 and 8051 are enjoying the same longevity Because there are a number of S 100 systems and other Z80 based CP M systems being actively maintained and repaired by their owners I decided to design a simple PIC based circuit that could emulate a Z80 for displaying memory writing to I O ports etc as an aid to troubleshooting Before I started the design I became aware of a product developed in the early 80 s by Nicolet Paratronics called the Z80 NICE It offered a lot more capabilities than I had planned to implement with only a small increase in component cost Using the capabilities of this device as a reference I designed the Z80 ICE to which this manual applies I have added some new capabilities as well which I hope will prove useful Many thanks to Jeff Jonas for the generous loan of his NICE unit so I could become familiar with it Chapter 2 Setup The Z80 ICE was designed to be used with either a terminal or a terminal emulation program such as TeraTerm or HyperTerm running on a PC or Mac Serial settings are 8 data bits no parity and 1 stop bit No
19. ables If maskable interrupts are enabled an I will be displayed If non maskable interrupts are enabled an N will be displayed If bus requests are enabled a B will be displayed Note that all three of these are always disabled in Quit mode regardless of what is displayed If Quit mode refresh bursts are being generated an R will also be displayed If start up Autorun is enabled an A will also be displayed Finally if the Z80 is currently executing instructions at full speed a Go command has been issued the word RUNNING will be displayed Format ST Example OK gt ST gt 0123 33 E P gt 0654 66 D P gt 0982 99 E P INBR Execution begins at gt 473F OK gt ST gt 0123 33 E P gt 0654 66 D P gt 0982 99 E P INBR RUNNING Z Sleep Causes the command processor to insert a variable delay before processing any other commands Format Z d8 The parameter is used to specify the desired delay in mSec The actual delay will be somewhat longer if refresh is enabled Q n eS PS Cee AO ee EG Chapter 6 Quit Mode Commands These commands can only be used in Quit mode Generate and display 16 bit checksum of memory region Display memory Examine a single memory location intended for scope loops Fill memory Go Input from I O port List disassemble memory Move memory block Memory test destructive Output to I O port Put data into a single memory location intended for
20. bled in Quit mode even if an I is displayed Format EI DI Disable maskable interrupts Prevents maskable interrupts from reaching the Z80 when in Go mode If this command is entered while the CPU is in Go mode interrupts will be disabled immediately Format EI Example OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR Tuy OK gt DI OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E NBR uvu OK gt EI OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR uvu EN Enable non maskable interrupts Enables non maskable interrupts to reach the Z80 when in Go mode If this command is entered while the CPU is in Go mode non maskable interrupts will be enabled immediately An N appears on the last line of the status display if non maskable interrupts are currently enabled All interrupts are always disabled in Quit mode even if an N is displayed Format EN DN Disable non maskable interrupts Prevents non maskable interrupts from reaching the Z80 when in Go mode If this command is entered while the CPU is in Go mode non maskable interrupts will be disabled immediately Format DN Example OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR uvu OK gt DN OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E I BR uvu OK gt EN OK gt ST
21. cates with the terminal through the RS 232 chip and controls the Z80 It is capable of reading Z80 register values loading the Z80 s registers single stepping the Z80 through code starting the Z80 running at full speed and stopping the Z80 The CPLD chip contains logic to allow the PIC to control the Z80 and also to inhibit the bus request and interrupt signals from reaching the Z80 It can also prevent the Z80 s MREQ IOREQ RD and WR signals from reaching the target system In Quit mode these four signals are forced to their inactive state in the target system to insure that the target system is not using the data bus This is necessary as the data bus is used for PIC to Z80 communication in this mode In Go mode the PIC chip starts up the Z80 and lets it run In this mode the ICE operates just like a normal Z80 chip In Quit mode the Z80 has been paused and can be used to implement the commands that give the ICE its power All communication with the target system s memory takes place through the Z80 To read data from a memory location the PIC arranges for the Z80 to read from that location and then hand the data to the PIC If the Z80 is halted it is not fetching op codes and cannot be controlled by the PIC chip This condition is detected and a message is displayed The system must be reset to restore normal operation Chapter 9 Watchdog Timer Z80 Reset Issue Some Z80 based arcade machines and pinball machines have a circuit call
22. ddress is entered current PC value is used I Input from I O port Input 8 bit data from selected Z80 I O port and display it Format I address 8 bit I O address entered as 1 2 hex digits L List memory Lists disassembles memory contents from start address to end as Z80 instructions Format L start end Addresses entered as 1 4 hex digits Both parameters are optional If no end address is entered 19 instructions will be displayed If no start address is entered display begins at the next address after the end of the last D or L command This is the saved memory address So entering just L will start displaying from the end of the previous L command Example OK gt 1 0 0000 F3 DI 0001 31 FO 80 LD SP 80F0 0004 3E A5 LD A A5 0006 32 00 80 LD 8000 A 0009 DD 21 00 80 LD IX 8000 000D DD 34 0A INC IX 0A 0010 FD 21 02 80 LD IY 8002 0014 FD CB 08 86 RES 0 IY 08 0018 OE 80 LD c 80 001A ED 78 IN A C 001c DD 36 10 69 LD CIX 10 69 0020 FD 22 06 80 LD 8006 IY 0024 DD CB 06 C6 SET 0 CIX 06 0028 3E 00 LD A 00 002A CB DF SET 3 A 002c 11 34 12 LD DE 1234 002F ED 53 OC 80 LD 800C DE 0033 21 00 00 LD HL 0000 0036 DD 21 00 00 LD IxX 0000 OK gt 1 003A 7E LD A HL 003B 4F LD C A 003c 06 00 LD B 00 003E DD 09 ADD IX BC 0040 2c INC L 0041 7D LD A L 0042 A7 AND A 0043 30 F5 JR NC 003A 0045 DD E5 PUSH IX 0047 DB 20 IN A 20 0049 D3 40 OUT 40 A 004B 76 HALT 004c c3 00 00 JP
23. dress Set breakpoint count Enable breakpoint Disable breakpoint Enable printpoint Disable printpoint Clear all breakpoints and printpoints Enable maskable interrupts Disable maskable interrupts Enable non maskable interrupts Disable non maskable interrupts Enable bus requests DMA Disable bus requests Enable refresh Disable refresh Enable start up Autorun setting saved in EEPROM Disable start up Autorun setting saved in EEPROM hexadecimal sum and difference Clock Frequency measurement Z80 clock Quit pause Z80 Repeat command line Status display Sleep insert delay BP Set breakpoint address Sets one of the three breakpoint addresses which are used by the trace and untrace commands Breakpoints end the current trace or untrace command when reached and enabled during either of these commands They are compared to the current PC after each instruction is executed Breakpoints only work in Quit mode Current breakpoint status can be displayed with the ST command Format BP n d16 nis 1 2 or 3 d16 is a 16 bit address Example OK gt ST gt OABC 00 D gt 0246 00 D gt 0369 00 D INBR OK gt BP 1 123 OK gt BP 2 654 OK gt BP 3 982 OK gt ST gt 0123 00 D gt 0654 00 D gt 0982 00 D INBR BPC Set breakpoint pass count Sets the pass count for one of the three breakpoint addresses which are used by the trace and untrace commands Count 0
24. ed a watchdog timer When code is executing normally the Z80 writes to or reads from a particular I O or memory address maybe a few times each second This action resets the timer and maintains normal operation If the CPU crashes it stops resetting the timer As a result the timer reaches a preset count which causes the RESETb input to the Z80 to go low resetting the CPU and restoring normal operation of the system If an ICE is used since the Z80 is paused a lot of the time the watchdog timer will not get reset and will keep resetting the Z80 and the PIC chip perhaps five times second or faster The ICE can t work if it keeps getting reset There are two ways that the ICE can be used in systems with a watchdog timer 1 Disable the watchdog timer Some arcade games have a jumper on the main board that can be used for this purpose You may need to solder across two pads temporarily to disable the timer Other systems may have a different way to disable the timer or no way at all 2 Modify the ICE to supply its own RESETb signal to the Z80 and the PIC chip If you do this you Il need to cycle power to the ICE to reset it since any target system reset switch will no longer function You can add a few components to the ICE PC board to implement a RESETb circuit Here is a schematic showing the modification needed There is already a place for bank sie the resistor on the ICE PC bd Ry C values shown are nominal
25. hardware handshaking is needed Note The R command can process data and store it in the target system s memory at up to 19 2 K baud if the target system is running at 1 MHz or higher If a slower Z80 clock is used higher baud rates can cause a data overrun condition which will cause an error message to be displayed Using hardware handshake won t fix this as the PC takes too long to react to CTS going inactive In this case simply switch to a slower baud rate The ICE automatically detects the baud rate After powering up the unit hit Enter on the terminal to send a carriage return The ICE uses this to detect the baud rate and set its rate to match Supported rates are 300 600 1200 2400 4800 9600 and 19 200 baud After the ICE has set its baud rate it will send the sign on message If you don t see this after pressing Enter reset or power down the system and try again Note The ICE s PIC microcontroller is reset by the same active low signal that resets the Z80 If there is a problem with the target system that causes this signal to stay low or float the ICE s microcontroller will be held in reset and will never send anything to the terminal The ICE will initially come up in Quit mode Z80 paused Press X to dump the registers and see if everything is OK If the register display hangs reset or power down the system and try again If you would prefer to have the ICE come up and start running automatically as a standard Z
26. med using Ctl S or Ctl Q or stopped by using Ctl C D Display memory L List memory V Verify compare memory T Trace U Untrace It is possible to put more than one command on the same command line In this case use a semicolon instead of carriage return to signal the end of a command Using the repeat line RL command it is possible to repeat a sequence of commands in a loop Delay can be inserted between commands with the Z command For example the command O 80 A5 Z 10 RL lt CR gt will write A5 to I O address 80 then delay for 16 0x10 mSec and repeat To break out of the loop press Ctl C The actual delay between iterations will be larger than 16 mSec if refresh is enabled The following commands always end command line processing and will prevent looping if used in a command line repeat loop G L Q R S T U W X Chapter 4 Overview of Operation The ICE has two modes of operation Go mode and Quit mode In Go mode the ICE executes Z80 instructions at full speed but not all of the commands are available Basically commands that don t require participation by the Z80 can be executed in this mode such as enabling or disabling interrupts or bus requests to the Z80 Breakpoints can be changed in Go mode since they are not used in this mode In Quit mode the Z80 is paused and can be used to implement the full set of commands such as displaying or disassembling memory computing checksums writing to I
27. o load hex data values into system memory No attempt is made to determine if write to memory was successful so you can substitute into EPROM but it won t accomplish much Format S d16 To advance to next address without changing contents hit CR To back up to previous address hit a dash To exit substitute memory mode hit a period SR Soft reset Causes the ICE to reset all of the Z80 s registers to zeroes Format SR T Trace This command may be used to step through target system code one instruction at a time The Z80 s internal registers are displayed after each instruction An optional parameter may be entered to specify a number of instructions to be executed Entering T 10 will execute 10 instructions and then stop If an enabled breakpoint is reached before 10 instructions have executed the trace will stop immediately If the number of instructions to execute is entered as 0 the trace instruction will continue until a breakpoint is hit and will not count instructions If no parameter is entered only one instruction will be executed If the Z80 encounters a Halt instruction when tracing it will stop fetching opcodes and will no longer be controllable by the ICE A message will be displayed in this case and the system will need to be reset to restore normal operation Format T d16 U Untrace This command is similar to the trace command but the registers are not displayed after every
28. the NICE unit implies that a maximum of 300 baud can be supported without hardware handshaking I haven t seen any problems loading files at much higher baud rates with no hardware handshake Operating current NICE draws about 500 mA from the Z80 socket Our unit draws about 70 mA with a CMOS Z80 installed and about 130 200 mA with an NMOS Z80 installed The PALs and MCU used in the NICE draw much more current than the CPLD and our PIC chip NICE supports assembly of Z80 instructions into RAM I don t This is a nice feature no pun intended but a lot of work which I couldn t justify It didn t seem useful enough to warrant the effort
29. uvu OK gt ER OK gt ST gt 0123 33 E gt 0654 66 D gt 0982 99 E INBR uvu EA Enable Autorun Enables Autorun after power up or reset This setting is saved in EEPROM and will be maintained even when power is removed Enabling Autorun causes the Z80 to immediately start executing code from address 0 at power up The ICE is in Go mode at this point Maskable and non maskable interrupts and bus requests are enabled The current Autorun setting is part of the status display Format EA DA Disable Autorun Disables Autorun after power up or reset This setting is saved in EEPROM and will be maintained even when power is removed Disabling Autorun causes the ICE to enter Quit mode at power up until a G command is executed Format DA Example OK gt EA OK gt ST gt 0000 00 gt 0000 00 gt 0000 00 INBRA ovg OK gt DA OK gt ST gt 0000 00 gt 0000 00 gt 0000 00 INBR 000 H Hex calculator Computes hexadecimal sum and difference If values entered are A and B in that order command displays A B A B Results are limited to 16 bits and will wrap above OxFFFF Format H d16 d16 Values entered as 1 4 hex digits Example OK gt H 10A5 674C 77F1 A959 OK gt H FFFE 0002 0000 FFFC OK gt H 2000 1000 3000 1000 CF Clock frequency Measure the frequency of the Z80 clock Results are displayed with
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