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Machine code First steps in Machine code There seems to be a myth surrounding ZX81 machine code. For some strange reason it is a common belief that programming in machine code is not easy. Indeed there are even people who would go as far as to call it difficult. Suffice to say this is not the case for, while it is true that the use of machine code was omitted from the Sinclair Manual, all you need is one little (BASIC) program taken from the book. Mastering Machine Code On Your ZX81. to get you started. Here it is . . . 10 20 30 40 50 60 70 80 INPUT X LET A*-" " IF A$ » " " THEN INPUT A$ IF A* -"S" THEN STOP POKE X. 16*CODE A$ + CODE A»(2)-476 LET X - X + 1 LET AS AS(3 TO) note there is nothing between "TO" and "I" GOTO 30 Now obviously there isn't enough room in this article for Machine code may seem bewildering, but Toni Baker — author of Mastering Machine Code on Your ZX81 or ZX80 — is convinced the whole subject is a piece of cake. Here, Toni attempts to convince you, with a clever screen-handling routine and the raw ingredients of a BREAKOUT game. me to teach the whole of machine code from scratch — that would be like trying to squash Sinclair's BASIC Manual into two or three pages — so instead I'll give you one or two little machine code routines which you can use in your own BASIC programs. Try this one. Load the above program, then add the following line: 1 REM 123456789023456789 Now RUN the program and input: 16514 "2A0C40" "0618" "23" "7E" "EE80" "FEF6" "2803" "77" "18F5" "10F3" "C9" Machine code address LD HL. (D FILE) LD B, twentyfour LOOP: INC HL LD A.IHL) XOR80h CP F6h HR Z.EXIT LD (HL).A JR LOOP EXIT: DJNZ LOOP RET Now please note — you do not need to understand what I've written in the right-hand col umn. All you need to do is enter what's written in the left column. When you've done that type "S" to stop the program. Now add these lines: 100 IF INKEY$ < >*' " THEN GOTO 100 105 IF INKEYt = " " THEN GOTO 105 110 RAND USR 16514 120 GOTO 100 46 ZX COMPUTING SUMMER 1962 ZX C Gf IK Sq M ad vo IK Mj Ca Pa 1K BR 36 I ST{
ie •chin* da add re si | )HL. .FILE) >8, '•ntyfour C HI l A.(HL) )R 80h >F6h IZ.EXIT ) IHL).A I LOOP INZ LOOP rr you do not what I've t-hand col do is enter ie left coldone that j program. Now type RUN 90 and just see what happens when you touch any of the keys. Incidentally, lines 10 to 80 can actually be deleted altogether now, and only line one is needed. From now on, any time the machine encounters the statement RAND USR 16514 the machine code magic will work. Try this little gem. Delete all the lines except line one. Now add the following lines: 10 FOR l«1 TO 100 20 PRINT 'three spaces followed by three inverse spaces'; 30 NEXT I 40 FOR I = 1 TO 50 50 NEXT) 60 RAND USR 16514 70 GOTO 40 Run this and stand back in amazement. For something a little more complex, here is a routine which will move a ball around a screen, bouncing it off walls and bricks. You can develop a kind of BREAKOUT-type game using this routine. Load the machine code loader at the start of the article and add one extra line: Quality SoPtuare I have bought numerous other items ot software Yours are excoHent They LOAD welt, have perfect nsltucnons the most user-friendly > have ever mei " IP R Noits) . 16K ROM Pack °;3V 1 * Imlall^e FtCf "GtlJIT lMVtDHtt- CMMtU sror mjrss — K COXMJ soon, ZXS1 sort-ware GALAXY INVAOERS 'requires minimum 4K RAM) in machine code Cassette and instructions £3 00 1K GAMES iDuck Shoot. Moonlander, Hangman, Crossword. Letter Square' Cassette arid instructions £3 00 "Just a short note to say how good your Space Invader cassette is i w4 programs descriptive and inferential stats) Cassette and instructions C3 00 "I acknowledge receipt of MULTIGRAPHICS and STATISTICS Having experienced nothing but trouble with s software, i was agreeably surprised by the good quality and flexibility of your products IV S Berks I 2X80 SOFTWARE ALSO AVAILABLE * Send s a e tor details, describing your system BRIDGE SOFTWARE IZ) 'Mail order ontyW 36 FERNWOOD, MARPLE BRIDGE, Eu,0 °~ n STOCKPORT, CHESHIRE SK6 5BE Work** top rem Machine code I REM 123456789012345678 901234567890123456 789012345678901234 567890123123456789 012345678901234567 890123 Now RUN the program and input the following (counting "/" as "newline"): 16516/0101/2A8240/3600/ 3A8440 3D 2002 23 23 2B 7E FE80/200B/2A8240/4A8440 ED44/328440/228240/3A8540 /3D/2006/11DFFF/19/1804/ II 2100/1 9/7E/FE80/200B 2A8240/3A8540/ED44/328540 /010000/7E/FE08/2009/03/ 3A8540/ED44 328540/228240 /3634/C9/S FE80/200B; 2A8240/3A8440 You can now delete lines 10 onwards. To demonstrate how this works just add the following BASIC: 10 PRINT "thirty-two inverse spaces" 20 PRINT "Inverse space thirty spaces inverse space" 30 as 20 40 PRINT "inverse space thirty graphic A inverse space" 50 as 40 60 FOR 1=1 TO 10 70 PRINT "inverse space thirty spaces inverse space" 75 NEXT I 76 80 90 100 110 120 PRINT "thirty two inverse spaces" LET X-PEEK 16396 + 256* PEEK 16397 + 200 POKE 16514.X - 256* INT (X/256) POKE 16515,INT (X/256) LET A-USR 16518 GOTO 110 Lines 10 to 76 just print the board. You can replace these by any board-printing routine you like. Lines 80 to 100 are absolutely vital for the machine code to work, (although the + 200 can be more or less + anything — it just determines the position of the start of the ball), and all the fun happens at 110 and 120. The instruction LET A a USR 16518 just moves the ball one square along. If you PRINT A afterwards you'll find it's always zero unless the ball hits a brick, in which case it will be one. So you see, the loop 110 to 1 20 is now really the whole of the 'game' It's up to you to improve it, but as long as you don't alter the machine code and just play around in BASIC, remembering that LET A « USR 16518 means "move the ball one square", it should be no trouble at all. SECOND FOUNDATION ZXUl SOFTWARE ALL OUR SOFTWARE IS ON CASSETTE AND DELIVERED BY RETURN CQMPUTATUNE TURNS THE IK zxei INTO A ONE OCTAVE ORGAN. STORING 100 NOTES PLAYS BACK TUNF AUTOMATICALLY - C 2 75 STARTER PACK TWELVE IK GAMES ON ONE CASSETTE, SEVEN MOVING GRAPHIC GAMES INCLUDING Road-Race. Subsearch, Tank-Shoot AND Pop. EXCELLENT VALUE - C3 90 ARCADE PACK FOUR ISK GAMES ON ONE CASSETTE - Surround. Tank-Shoot Spider Chase AND Tenpin Bowling C3.90 VARIED GAME PACK FOUR I6K GAMES. Jaywalker. Car-Crash. Smargana AN0 Fox and Hounds. CAR-CRASH" IS MACHINE CODE AND WORTH C3.90 ALONE! ALL FOUR GAMES C3 90 TOLINKA - isK USE YOUR zxai AS A CHESS GAME RECORDER FEATURES TOO NUMEROUS TO MENTION C3.90 G.C.E. EXAMS 180 MIN EXAM IN O LEVEL PHYSICS OR MATHS - GIVES GRADE AND DETAILED REVISION PROGRAMME C3.90 EACH Prices are inclusive (Overseas add £1 00 P&PI Send sae for details, or cheque with order to SECOND FOUNDATION. 22 Bramber Belgrave, Tamworth Staffs B77 2LL MMER 1962 ZX COMPUTING SUMMER 1982 47
Page 1 and 2: j Summer Britain's Biggest Magazine
Page 3 and 4: ZX 80/81 HARDWARE/SOFTWARE ZX KEYBO
Page 5 and 6: ZX Computing is published quarterly
Page 7 and 8: 16K-byte RAM pock for massive add-o
Page 9 and 10: The @*?$1!&£@ RAM pack Dear ZX Com
Page 11 and 12: I u < o •0 8 & £T © Benchmarks
Page 14 and 15: 1 1© L" 20 30 IN5 5 0 60 80 9C 100
Page 16 and 17: The Explorer's Guide to the ZX81 IF
Page 18 and 19: Orbit S M King from Bristol takes y
Page 20 and 21: ID 15 20 25 30 35 4G> LBV 5 NMER RE
Page 22 and 23: E" OR Pi="M" THEN GOTO 785 CO)TO 7"
Page 25 and 26: I first became aware of the bug in
Page 27 and 28: A. Beasley After using the ZX80 for
Page 29 and 30: I sr The first few weeks after the
Page 31 and 32: i! I are odd jmeone to write a a ta
Page 33 and 34: id (and IC AND )MPUTER" er and >ut
Page 35 and 36: 16K Games Power Boat if you're desp
Page 37 and 38: }RTIO 3RT W J Hfl'.f K E COl T CORj
Page 39 and 40: 1220 \225 230 250 ,L NEED m 270 WAY
Page 41 and 42: IKING >S TO THi 350 >TCARD Ol OF 84
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Page 57 and 58: Winning Positions COIN COIN BELL BE
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Page 61 and 62: lTURES P&P) ITAL iGUE write to IGHT
Page 63 and 64: ms, arid I time you convince somebo
Page 65 and 66: ist for the feel good luct their 5
Page 67 and 68: *t»m Tarshis, Executive Vice Presi
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Page 71 and 72: tng of KE, the the his mg ay. cts i
Page 73 and 74: Review Keyboard Review Crofton's Ad
Page 75 and 76: "The hi-res board seems to go to a
Page 77 and 78: Make the most of IK Chopper Squad R
Page 79 and 80: onic Systems 80/1 ^ / RAMPACK MASSI
Page 81 and 82: 51 IF A(2) «* 188 THEN LET A (Z)
Page 83 and 84: 4110 IF (A(Z - 13) = 1 OR A(2 - 13)
Page 85 and 86: ZX81 HARDWARE 40 KEY KEYBOARD. Kit
Page 87 and 88: 4090 GOTO 9100 5000 GOSUB 9500 5010
Page 89 and 90: I 1K Games 10 LET 20 LET 30 LET 4-0
Page 91 and 92: Etchasketch This very short program
Page 93 and 94: meant the addition to its repertoir
Page 95 and 96: SYSTEM/MULTIFUNCTION COMMANDS BREAK
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270 280 290 300 310 320 IF IF IF IF
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Make sure you get every issue of ZX
Page 101 and 102:
ZX80 Programs ZX80 fights back Musi
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Catch Avoid being trapped by your s
Page 105 and 106:
Software Orwin strikes again Casset
Page 107 and 108:
ZX81 Software LARGE CHARACTERS REM
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Moving graphics Getting into the Mo
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Specialist Book§ i Choosing progra
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WHAT CAN I DO WITH 1K? If your answ
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Compiler A program whose function i
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ZX COMPUTING SUMMER 1982 Computer G
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S-100 Name of a bus or connection s
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After taking your move the computer
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WHAT'S ON NEXT? IN HOBBY ELECTRONIC
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are not lost when the ZX81 is turne
Page 131 and 132:
ZX Users' Club JOIN YOUR USERS' GRO
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