BY PHYLLIS COLE, iGNTOR
Contents
1. PET photo courtesy of Utter Chaos Commodore s PET is a factory assembled personal computer based on a 6502 microprocessor The unit includes a key board cassette tape unit CRT some graphics upper and lower case and an extended 8K BASIC The system with 4K of user memory costs 595 the 8K model costs 795 For details see the last 2 issues of People s Computers Until there s some sort of formal PET Owners organization People s Computers will provide space each issue as a forum for PET people The name of the forum will be SPOT Society of Pet Owners and Trainers unless something better comes along Possible uses for the forum include swapping software and ideas PET pro jects and maybe Teachers PET and complaints obviously PET Peeves Per haps projects that involve hooking the PET to other devices should come under the heading ComPETible Stuff TEACHERS PET The we of this article refers to a group of computer professionals including your editor who have purchased a PET as part of a project aimed at integrating computers into the daily routines at a local school To date we ve concentrated on preparing a wide variety of sample programs that we ve shown to both kids 16 PEOPLE S COMPUTERS and teachers As of January we ll begin workshops with teachers and junior high age students to teach them how to program in a version of PILOT The workshops will focus on the development2. with printing in reverse i e white on black To help make PET listings more readable we ve decided to indicate special stuff inside square brackets using commas to separate items Sometimes a number precedes an item to tell how many times it should be repeated We use HOME CLR RVS OFF and INST as shown on PET keys Sometimes SPACE is used to show where a space should be typed A single character indicates that the graphic shown as the shifted character should be used Examples are provided in Figure 1 Finally you may have noticed colons at the beginning of some program lines Colons indent lines inside FOR loops to help show the limits of the loop Listing says You type PRINT CLR key shift Q PRINT CLR Q PRINT HOME 3 DOWN S PRINT HOME key cursor down 3 times 3 black Qs on white shift S STARS Here s a familiar number guessing game that we ve adapted for the PET The pro gram randomly selects a number from 1 to 100 for you to guess You try to guess the number then the program prints out from 1 to 7 stars asterisks depending on how close your guess is When you guess the number the screen goes blank then 40 stars are randomly displayed in the top 20 lines of the screen 8 00 oo 17 gt 0 6 ae ek Se a 62 eek e285 What happens when program The screen shows is run PRINT Cursor goes black heart on white home upper white dot on black left and g scree
3. of a body of programs to support the topics that will be studied in the latter half of the school year in the junior high In addition some programs for younger kids will be developed the junior high school will serve as a primary resource for introducing the PET and PILOT to others in the school We plan to include even nursery school age children in the project already we have a demonstration program for youngsters that age RoN l TAPE TIPS We ve found that the most reliable tapes to use on the PET are Maxell TDK and Memorex We ve had some problems with the cheapest Radio Shack tapes We definitely do not recommend Scotch tapes we confirmed reports that when used as computer tapes they snag although the problems of snagging may be reduced if very short tapes are used In its manual Commodore recommends using Nortronics Brand tape head clean er They recommend Nortronics Hand de mag and Robins brands of head demagnetizers Tape deck head cleaning and demagnetizing needs to be done every 50 100 hours of tape running time or when you have trouble reading tapes reliably SOFTWARE AVAILABILITY PET programs are beginning to be adver tised let us know which ones you ve tried and whether you recommend that others purchase them Some of the programs we ve been working on are now available For a description of the pro grams a price list and a licensing agree ment se
4. without changing the picture get rid of the drawing symbol by pressing either of the CRSR keys then use the digit keys to move the target When you are ready to draw again press a graphics key or RVS When you want to admire your drawings without the target cell blinking at you periodically press RETURN Then to make it blink again type any other key S is a good choice To move the target to the center of the screen press HOME To start a new picture press CLR note that you ll have to shift To stop drawing so you can do something else with your PET first press RETURN and then press STOP Saving and Retrieving Pictures When you re ready to save a picture type the left arrow cursor control key i e the one that points to the tape recorder First the cursor stops blinking while your picture is measured during the 30 seconds or so that this takes little streaks of light may dance about the screen Next the first 3 lines of your picture are erased and you re asked SAVE FILE NAME Type in a name for your picture and press RETURN and then you ll be told to press RECORD and PLAY on the recorder It ll take about a minute more or less depending on the size of your picture to save your picture on tape When saving is complete the program clears the screen and displays the initial drawing symbol a dot in the center of the screen Now rewind the tape To retrieve your picture from tape and print it on
5. POKE The program will run on either a 4K or 8K FET The Target The program treats the screen as a grid of cells 38 across and 24 down When it starts it clears blanks the screen and displays a large round dot the drawing symbol in a cell near the center That cell is the initial target cell A white square blinks at you occasionally to let you know where the target cell is To draw a picture made of dots use the program s target motion keys They are not the same as the PET s cursor keys Instead the digit keys 1 through 9 are used to make the target move one cell in any of eight directions Pretend the target cell is on the S key To move it left press 4 to move it up and right press 9 and so on When ever the target moves it will inscribe the drawing symbol in its new cell The Drawing Symbol When you are tired of dots press any graphic key Shifting is only needed for the graphics on the 1 9 key The graphic character on the key will become the new drawing symbol It will be inscribed in the target cell Press RVS and the color of the drawing symbol will be reversed Subsequently chosen drawing symbols are not affected 18 PEOPLE S COMPUTERS To erase make SPACE be the drawing symbol The reverse SPACE draws white stripes DEL erases the target cell without changing the drawing symbol You can un DEL using the F key Other Features To move the target
6. the screen type the up arrow cursor control key the one that points to the screen Notice the save cursor left and retrieve cursor up commands involve shifting hopefully this will help avoid accidental typing of these commands Annotations Here are brief descrip tions of major elements of this program variables LX MX LY MY least and maximum X and Y used X Y L target X Y screen location GR R drawing symbol graphic and reversal PG PR previous graphic and reversal from location L SC screen cursor address WH PL WT FL blink timers white black wait flash Character codes SP space SS shift space CV screen ascii conversion factor SH shift bit US unshift mask BY byte mask OT quote CRe carriage return RE reverse DE delete R initial reverse OFF XR exchange reverse XR OFF RVS line s 5 puts system into graphics mode as opposed to lower case mode 6 20 sets up constants initializes variables note that the first and last characters in strings H and V are cursor controls 30 sets initial drawing symbol to a dot shift Q and clears the screen 40 60 prints dot in the center of the screen 100 looks for keystroke 150 converts keystroke to unshifted ascii 200 checks that the target is blinked off 250 RETURN causes a long blink 300 resets short blink 400 800 handles number key graphic key DEL RVS and the cursor control keys 850
7. the size of the cat affects the size of its pounce
8. things can happen as a result of a pounce depending on the relation between the size of the pounce and the dis tance between the animals 20 PEOPLE S COMPUTERS AT s Ott St as fat x Eg og er SS as s 5 ae 4 Yi ey A Ai 1 If the size of the pounce matches the distance The cat lands on the mouse and catches it and the game ends 3 3 POUNCE 1 YOU VE CAUGHT THE MOUSE WITH 5 POUNCES WANT TO CHASE ANOTHER MOUSE YES 2 If the size of the pounce is smaller than the distance The cat approaches the mouse but doesn t get it POUNCE 15 s 3 If the size of the pounce is greater than the distance The cat jumps over the mouse landing on the other side In order for the play to remain on the paper the whole frame of reference is shifted to the right 333 EPPP POUNCE 17 ee 2233 Since the cat always pounces toward the mouse the player doesn t have to worry about direction when making pounce decisions 4 Sometimes when the size of the pounce is almost the distance to the mouse the mouse runs away POUNCE 4 T2333 O8O OH OH THE MOUSE SEES THE CAT RUN MOUSE RUN PPPE 3333 A small percentage of the time that the mouse runs it will run into its hole Then the game ends with the mouse the winner Two runs are on the opposite page Notice that the sizes of the cat and mouse can vary between games Notice too how
9. 875 the LEFT cursor causes a save on tape UP retrieves from tape 1000 encodes symbol for display 1200 resets drawing symbol 1250 reverses drawing symbol 1300 1500 displays symbol in target cell 1700 2275 moves target in direction indicated by number key 2300 locates new target 2325 stores previous graphic 2350 stores previous reverse information 2400 checks for drawing symbol 2500 2700 blinks the target if there s no symbol to draw 3000 3020 blinks the target while you re not doing anything 4000 4020 reverses the color of the target cell 4500 4510 handles delete DEL key 5000 initializes variables used in storing the picture on tape 5010 5130 determines the size of the picture 5500 5615 saves 3 lines of the picture in an array 5618 5627 clears first 3 lines of the screen 5630 5635 requests file name for the picture 5640 5700 stores picture onto tape Lines 5675 5677 turn the tape recorder motor on for 3 jiffies 3 60 second and then off This code is needed on y for early PETs which tend to have trouble reading data files This technique should be used every 191 characters 1 record or as here more often 6000 6015 opens file reads X1 and Y1 coordi nates checks status bit to see if end of file reached 6020 6040 positions picture screen 6050 6100 reads and prints picture closes file in center of 1 REM PET DRAWING PROGRAM 2 REM c 1977 PENINSULA SCHOOL 3 REM PERMISSIO
10. IN CHARGE 130 PRINT OF THE STARS HERE PLAY MY GAME OF 140 PRINT STARS AND GET SOME STARS FOR 150 PRINT YOURSELF PRINT 160 PRINT I WILL THINK OF A WHOLE NUMBER FROM 170 PRINT 1 TO 100 YOU TRY TO GUESS IT THE 180 PRINT MORE STARS I PRINT THE CLOSER YOU ARE 190 PRINT IF I PRINT 7 STARS YOU ARE 200 PRINT VERY VERY CLOSE 205 PRINT PRINT 210 PRINT OK STARSEEKER I M THINKING OF A NUMBER 220 X INT 100 RND 1 1 N 1 230 PRINT 240 INPUT WHAT S YOUR GUESS G 250 IF G X THEN 400 260 D ABS G X 270 FOR Q LOG D LOG 2 TO 6 280 PRINT 290 NEXT Q 300 N N 1 GOTO 230 400 REM GOT IT 405 PRINT CLR 410 FOR Q 1 TO 40 420 Y INT 800 RND 1 1 POKE 32768 Y 42 430 NEXT Q 440 PRINT HOME 21 DOWN 450 PRINT YOU GUESSED MY NUMBER IN N TRIESI I 460 PRINT PRINT PRESS RETURN TO PLAY AGAIN 470 PRINT PRESS ANY OTHER KEY TO STOP 480 GET A IF A GOTO 510 490 IF ASC A 13 GOTO 205 500 PRINT PRINT BYE FOR NOW 510 END PRINT JAN FEB 17 DRAW UPDATE In our last issue we published a program DRAW that allows you to draw pictures on the PET Even young children can quickly and easily learn to use the PET s graphic characters using this program Now we ve added to the program You can save on tape and retrieve the pictures that you draw We ve also modified the program to PRINT the characters on the screen instead of using
11. L 1 TO WT NEXT DL 2700 GOSUB 4800 2800 GOTEC idv IAGO FLESTES 2019 IF FLEWH THEN GOSUB 4000 3020 IF FL Bl THEN FL 0 GOSUB 4000 3030 GOTO 100 ANON PR XR PR PRINT CHRS CPR 4010 PRINT BGS 2 7 LOPT I 4920 RETURN 4500 POS PREIR 4570 PRINT Olt SPACL LEFE Y s CHRSER 4h7u GOO Ta SOON X Xi LX YOSNVe Y1 Y K eSC NOTO L R Y Y IQ RY 5020 lt b OR X20 1039 HOBO Cro ee lt CEPLER K K Kt1 G SP GOTO 5180 DOGU oL X lt XO THEN X0 X GAJA lt FF XOXNT THEN XTA HOO 62 HASO PET SAUNA AEO a E A E TEL YT SLOG ANEETA 5130 NEXT Y 5500 SY 0 5510 FOR Y YO TO Y1 5512 K SC 40 X0 SETS RVR Loa 5629 OR X X0 TO X1 5530 C PEEK K SP AND CV SS 535 22 eC BY PE VeRV GOTO 545 5540 RV V LS LS MIDS PRVS OFF V 2 1 5545 MKEK I LS LS CHRS SH RV C 56 00 2HEXT X SEIU EASYJET S eS741 BRELES 2d SY lt 3 AND Y lt i GOTO 5685 5620 IF Y gt 0 2 GOTO 5660 5625 PRINT HOME OFF 5626 FOR I 0 TO 2 FOR J 0 TO MX 5627 PRINT NEXT J PRINT NEXT I 5630 INPUT HOME SAVE FILE NAME NM 5635 PRINT HOME 5640 OPEN 1 1 1 NM 5650 PRINT 1 Y1 1 Y0 5655 PRINT 1 X1 1 X0 5660 FOR I 0 TO SY 1 5665 PRINT 1 QT E I QT 5670 7ES 2 s 5675 POKE 59411 53 T TI 5676 IF TI T lt 3 GOTO 5676 5677 POKE 59411 61 5678 NEXT I 5680 SY 0 5685 NEXT Y 5690 CLOSE 1 5700 GOTO 30 6000 OPEN 1 6005 INPUT 1 Y1 6010 INPUT 1
12. N TO USE BUT NOT SELL 5 POKE 59468712 0 C232768 S P 32 SS 160s CVTS 7 BY 255 SH 128 US 127 QT CHRS 34 8 LXe1 MX 53 LY 0 MY 24 DIM E 2 9 HS LEFT P eCHeSroye RIGHTS 10 VS PUPTECHPS 0 4 DOWN J 16 NIS 1 Tse cael 3 KEATS BESO 20 WHe5O Bleo3 Web XR 164 TR L4b 30 GRS O12 4 PRINT FCLERT 40 Y INT MY LY 2 X INT MX LX 2 45 R IR 50 PRINT HOME LEFTS 12 DOWN Y SPC X 60 GOTO 2300 100 GET CS FF C s GOTO 3000 150 C ASC C AND US 200 IF FL gt WH THEN GOSUB 4000 250 JF C CR THEN FL 1E8 GOTO 100 300 FL WH WT 400 IF CS gt N1 AND C lt N9 THEN 1700 450 IF C gt SP GOTO 1000 500 IF C DE GOTO 4500 600 IF C RE GOTO 1200 700 IF CS DOWN OR C RIGHT THEN R IR GR 750 IF C HOME THEN GR GOTO 40 800 IF C CLR GOTO 30 850 IF C LEFT GOTO 5000 875 IF C UP GOTO 6000 990 GOTO 100 1000 GR CHR C SH R IR 1100 GOTO 1300 1200 IF GRS THEN GRS PG R PR 1250 R XR R PRINT CHRS R 1300 PRINT GRS LEFT 1500 PG GR PR R 1600 GOTO 100 1700 PX X PY Y 1750 X X C 1 3 INT C 2 3 1800 IF X lt LX THEN X LX 1900 IF X gt MX THEN X MX 2000 Y Y 1 INI C 49 3 2100 IF Y lt LY THEN Y LY 2200 IF Y gt MY MY 2250 PRINT MID HS X PX 2 1 2275 PRINT MIDS VS Y PY 2 1 23900 L SC 40 V X 2325 PGS CHRS PEEK L OR SH 2350 PR IR PELK L AND SH 2400 IF GRS lt gt GOTO 1300 2500 GOSUB 4000 260 FOR Dl
13. X1 6015 IF ST GOTO 6100 6020 YO INT MY LY 1 Y1 2 1 6030 XO INT MX LX 1 X1 2 1 6040 PRINT MIDS CLR 12 DOWN 1 Y0 6050 FOR Y 1 TO Y1 6060 INPUT 1 L 6070 PRINT SPC XO LEFT L 6080 IF Y lt MY THEN PRINT 6090 NEXT Y 6100 CLOSE 1 6110 GR 6120 GOTO 40 OTHER STUFF We ve made our first use of the 8 bit user port we can flash a 40 watt lamp on and off under program control The circuit we used is from The First Book of Kim which is reviewed in this issue The 115 volt AC circuit must be isolated from the 5 volt digital circuit We used a 1 50 opto isolator to do this and a 1 40 Triac electronic switch to operate the lamp We ve also used the PET to assist in analy zing data from a questionnaire The program is designed so that inexperienced non programmers can easily enter data using one DATA statement per question naire For easy reference the DATA statement line number is the same as the sequential identification number assigned to each questionnaire Checking the data after it was entered into the computer was facilitated by a program that displayed data for any specified questionnaire in an easy to read form The PET and its associated questionnaire analysis programs have attended various meetings where survey results were discussed To the delight of all concerned questions such as What happens if we change factor X by amount Y and What s the median of Z
14. ing together two long time supporters of People s Computers Mac Oglesby is a teacher in Vermont from his time sharing terminal in a log cabin he creates games for classroom use Weve published many of Mac s kid tested games over the last few years Joanne Verplank the Director of Community Computer Center has introduced thousands of kids to computers over the last few years Here she shares with our readers her exper iences with one of her favorite games Mac s POUNCE We have to estimate and compare visually all the time while driving walking or giving directions in order to buy raw materials or decide which supermarket line is the shortest However visual skill building which includes estimation and comparison is often ignored in schools POUNCE an amusing chase game by Mac Oglesby offers a chance for us to practice estimating and comparing short distances POUNCE can be used by players at several levels of experience Beginners easily learn to play yet the game has enough variety to chal lenge the more advanced WHAT HAPPENS Players are shown representations of the cat and the mouse CAT MOUSE When the game begins the mouse is at the left margin and the cat is some distance away The computer prompts POUNCE waiting for a number to be typed 3 POUNCE The cat pounces toward the mouse moving a distance corres ponding to that number in this case 4 4 Hae POUNCE Several
15. n clears white dot printed in home position PRINT black S on white Cursor goes home then down 3 times white heart on black i e to row 4 next prints a white heart Examples of Notation for Special Characters Figure 1 100 sets lower case mode 110 clears the screen moves the cursor to second row 120 210 prints out the instructions 220 selects X the random number to be guessed 230 240 gets the guess G 250 branches to line 40 if the correct number was guessed 260 calculates D the distance that the guess G is from the correct answer X 270 290 loops to print from 1 to 7 stars depend ing on the value of D D 1248 16 32 64 Oo T2353 4 amp 6 No F 6S 4 a2 300 gets next guess 405 clears screen 410 430 loops to print 40 stars in randomly chosen locations in the first 20 rows of the screen In these 20 rows there are 40 20 or 800 locations to choose from We ran domly select Y an integer from 1 to 800 The command POKE 32768 Y 42 prints an asterisk ascii code 42 in the Yth loca tion on the screen 440 490 moves the cursor home then to the 22nd row the second blank line prints a message about how to restart the game 500 waits until something is typed from the keyboard 510 530 if RETURN was pressed starts the game again if anything else was typed ends the game 10 REM STARS 100 POKE 59468 14 110 PRINT CLR DOWN 120 PRINT WELCOME TO MY GALAXY I M
16. nd a stamped self addressed envelope to Computer Project Peninsula School Peninsula Way Menlo Park CA 94025 DIAL A PET We ve used a board from The Net Works see announcement section to connect our PET over the phone to other com puters and so we got the listings that accompany this article The PCNET Personal Computer Network Committee is involved in setting up protocols standards to enable different kinds of home computers to communicate with one another We re implementing the protocols on the PET in BASIC Using Commodore BASIC and The Net Works board we can barely keep up a 30 character per second speed However we expect to be able to implement all the PCNET protocols in BASIC So far our PET can automatically dial the phone and can receive and acknowledge packets of information See Computer Networks by Larry Tesler Volume 6 Number 2 Other folk are implementing them on other home computers often in assembly language You ll be hearing more of these efforts in later articles To receive the latest draft of the PCNET protocols send 3 00 to cover replication and mailing costs to Dave Caulkins 437 Mundel Way Los Altos CA 94022 NOTATION Most printers can t print PET graphics Also Commodore BASIC lets you put cursor control characters into PRINT statements and inside the quote marks displays special reverse characters when you do so And most printers can t cope
17. were readily answered and when appropriate the results were displayed as a graph When the questions involved complex calcula tions whose results were not obvious the computerized approach saved many hours of analysis and most likely forestalled many hours of discussion since in a brief time period it was possible to explore many possible alternatives in depth A nice feature we ve only recently discovered you can list programs at a readable speed about 2 lines per second by holding down the RVS key while doing a listing For more tips and another PET program see the letters section of this issue We ve seen draft versions of an introduc tory PET manual and a tutorial tape which introduces BASIC Both are written for the novice The tape s 10 lessons go into more detail than does the manual I learned useful new information even with a brief glimpse at the tape you don t need semi colons to separate items in a PRINT statement PRINT HI N works fine The PET User s Manual now being written promises to be the more complete work that many of us await Commodore isn t even guessing when documentation will be available Last but not least we hear that as of the first week of December Commodore was producing 100 4K PETs a week and an unknown number of 8K systems sna RA JAN FEB 19 PROGRAM BY MAC OGLESBY DISCUSSION BY JOANNE KOLTNOW VERPLANK Community Computer Center In this article we br
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