Mixed Game Bag III

Date: 1983
Type: Cassette
Platform(s): TS 1000
Tags: Game

Mixed Game Bag III is a collection of three arcade-style games — Blitz, Freeway Crossing, and Rats/Snake — packed into a single program listing with each game stored as a separate SAVE block. Each game uses machine code routines called via USR to handle the core gameplay logic, with BASIC handling display, scoring, and input. The Blitz game generates randomized city skylines using block graphic characters and string slicing, while Freeway Crossing uses SCROLL for vertical screen movement and tracks a high score across sessions using a variable. The Snake/Rats game boots directly into machine code via RAND USR, with BASIC only managing the play-again loop.

Program Analysis

Program Structure

The listing contains three independent games, each with its own line 1 REM block containing embedded machine code or data, its own SAVE statement, and its own entry point. The three games are:

  1. Blitz — a city-bombing game (lines 50–2020)
  2. Freeway Crossing — a road-crossing game (lines 1–1100, second program block)
  3. Rats / Snake — a snake-style game (lines 3–520, third block; lines 9–30, fourth block)

Each game’s line 1 REM statement serves as a machine code store, a well-known technique for embedding binary routines in BASIC programs without using separate memory areas.

Machine Code Usage

All three games rely heavily on USR calls into machine code stored in the REM lines:

  • Blitz calls USR VAL "17105" at line 300 to run the main game loop, and USR VAL "16514" is polled indirectly via PEEK in Freeway Crossing.
  • Freeway Crossing uses USR 16514 at line 38 to detect collisions, branching to line 500 on a nonzero return.
  • The Rats/Snake game at line 10 calls RAND USR 16562, handing almost all control to machine code; BASIC only manages the play-again prompt.
  • The POKE VAL "16753",U in Blitz (line 80) and POKE VAL "17209",U in Rats (line 82) write a user-supplied speed value directly into the machine code routine, providing a difficulty control.

Using VAL "number" inside POKE and USR is a memory-saving idiom: storing the number as a string in a VAL expression avoids the five-byte floating-point constant that would otherwise be embedded in the BASIC line.

Blitz — Key Techniques

The city skyline in Blitz is generated procedurally at lines 100–160. The outer FOR U loop iterates across columns; for each column a random height Z is computed, and an inner FOR Y loop prints block graphic characters to build the building. Line 125–126 construct the bomb/explosion sprite string A$ by slicing a master string of block graphic characters using SGN PI + RND * CODE "£" as the index, producing varied visual effects.

  • Line 152 conditionally prints a solid block ("███") using the AND RND<RND idiom — when the condition is false, AND returns the empty string, printing nothing.
  • Line 153 similarly prints a partial explosion graphic with probability controlled by RND<VAL ".3".
  • Line 810 uses PEEK VAL "16515" and PEEK 16514 to read the bomb’s screen coordinates back from system variables updated by the machine code routine.
  • Score display at line 820 uses CODE "?" (which equals 63, a column position) as a literal constant, avoiding a stored numeric value.

Freeway Crossing — Key Techniques

The player character is drawn using conditional string expressions at line 42. Three separate AND conditions select between different graphic characters (▞, ▌, ▐) depending on the fractional part of G and the current key pressed, animating a walking figure. The variable G is incremented by 0.5 each cycle; G=INT G tests whether G is a whole number, toggling the animation frame.

  • Traffic is generated at line 105 with W=1+RND*12+(15 AND (G=INT G)), placing cars at random horizontal positions with a lane offset on alternate frames.
  • Two SCROLL calls at lines 120–122 advance the road by two lines per tick, increasing apparent speed.
  • The high score M persists across rounds within a single run, stored as a plain variable and compared at line 260.
  • Line 255 has an anomaly: PRINT AT R+CODE "▝",P;"▟";AT P,P;"** CONGRATULATIONS **" — the second AT P,P uses the horizontal position variable as both row and column, which may place the text incorrectly for most values of P.
  • Line 290 uses GOTO PI — since PI ≈ 3.14159, this rounds to line 3, which does not exist; control falls through to the next available line. This is intentional flow control.

Rats / Snake — Key Techniques

This game is the most machine-code-centric of the three. The BASIC wrapper is minimal: RAND USR 16562 at line 10 launches the game, and lines 12–15 handle the play-again prompt on return. Lines 90 and 130 draw the top and bottom border rows using repeated bracket and tilde graphic characters printed in a single PRINT statement, constructing the maze walls before handing off to machine code.

  • The PRINT AT CODE "+",SGN PI at line 130 uses CODE "+" (= 43) for the row number and SGN PI (= 1) for the column — both are constant expressions evaluated at runtime, saving storage versus numeric literals.
  • Line 510 prints either “YOU WIN” or “I WIN” using two AND conditionals on the USR return value U, a compact alternative to an IF/ELSE structure.
  • RUN at line 520 (without a line number) restarts the entire program from the beginning, resetting all variables — used here as a clean game-restart mechanism.

Common Idioms Across All Three Games

IdiomPurpose
CODE "x" as numeric constantSaves 4 bytes vs. a stored floating-point number
VAL "number" in USR/POKE/GOTOAvoids 5-byte FP constant in BASIC line
SGN PI for the value 1Compact constant expression
INT RND for the value 0Always evaluates to 0 since RND ∈ [0,1)
string AND conditionConditional print without IF statement
Machine code in REM line 1Stores binary routines in addressable BASIC memory

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Blitz, Rat’s Nest, Snake, Sketch Pad, Cross the Road. Bomb targets (Blitz), trap your opponent (Rat’s Nest) and more. 2K.

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Source Code

  10 REM  ▛ ▘ Q L PP,)▐PP ▘ ▘   #  5[>]RND)▙RND▘,,  GOSUB [K]TAN 5▙RNDO# RETURN4S£Q 7O5[,,]RNDP▘▘▘TAN ▘  TAN LN [V]▝Y LOAD [X]4C[W]C0Y TO [W]44U▜RND[R]C▖ RETURN▌S-5▄RNDO# RETURN<S$▘ CONT ▀TAN 5▄RND# RETURN▝S▘P GOSUB #▙RNDLN  PRINT ▒E:RND##[R]C£ RETURN▙C▒ RETURN#C▖▘  TAN )5 ;#[R]C▒ RETURN▙C▖ RETURN#4 GOTO 7#[R]C▒ RETURN▄C▖ RETURN#4 TO 7#[R]C▖ RETURN#4CHR$ /▀█▙▄ GOSUB #▙RNDLN  PRINT ▒)PINKEY$ ▘▘ LN #" GOSUB #▙RND▖LN  PRINT ▒)OINKEY$ ▘▀ LN #"LN [V]▝# RETURN CLEAR4(# RETURN LOAD 4"U▜RND[R]4▌5▜RNDQ▘:▛VAL LN [V]▝AT £4 SAVE LN NOT PI ▘,,,,TAN     GOSUB #▙RNDLN  PRINT ▒)▙INKEY$ ▘▘ LN #" GOSUB #▙RND▖LN  PRINT ▒)▙INKEY$ ▘▀ LN #"▘,,,,TAN 5▜RNDO# RETURN▝4:U▙RNDM[$]RNDU▄RNDWWM[:]RND5▜RNDY▒[Y]K▘#/▛▀▀▄▚▚▌▐5ASN INKEY$ - U▜RND#;#M[?]RND GOSUB #[$]RNDLN  PRINT ▒)▙INKEY$ ▘▘ LN #"5[$]RNDU▜RND RETURN▒K▘O#  RETURN4S▘O# RETURN4S▖Q 7O5[:]RNDU▜RND RETURN▌S▘O# RETURN+S▖[J]M▜RND▘,,,,TAN  GOSUB #[$]RNDLN  PRINT ▒E:RND#[R]C▖ RETURN#4▖▘▖▖TAN ▘,,,,TAN E:RNDQ▒Q [J]M▜RND5▗RNDOTAN )[?]RND▘▘ LN #"TAN LN [C]RND#[L]C▖#[L]PITAN U[,,]RND[R]4▖#[5]PITAN LN AT RND# RETURN▀COS #[L]4▖#[5]PITAN U▜RND[R]CODE [,,]PILN ▐INKEY$ #[A]PILN [E]INKEY$ U▜RND[R]COS LN 8PIY▖[S]C▖LN YPITAN LN #PITAN  GOSUB #▗RNDTAN U▄RND RETURN< AND #PI# SLOWRNDE£RND)▛ ;P# RETURN.TAB #PIQ9FP# RETURN.TAB #PIQ 7Q #[5]PILN [0]RND##PIE£RND GOSUB #ORND# NEW▘#;# RETURN["]"")5  GOSUB ##[R]""Q["]TAN  "▝  REM 
  50 SAVE "BLIT[Z]"
  60 PRINT "SPEED ? (1 TO 255)"
  70 INPUT U
  80 POKE VAL "16753",U
  90 CLS
 100 FOR U=SGN PI TO CODE "="
 110 PRINT AT U,CODE "3";" "
 120 LET Z=VAL "1.33"*U+(RND<RND)
 125 LET A$="▛▜▒█[▒][~~][,,]["][:]["][-][=][=]"(SGN PI+RND*CODE "£")
 126 LET A$=A$+"▒█[▒][~~][,,]["][:][-][=]["][O]"(SGN PI+RND*CODE "~~")+A$
 131 FOR Y=INT RND TO RND*RND*CODE "?"
 140 PRINT AT CODE "="-Y,Z;A$
 150 NEXT Y
 152 PRINT AT CODE "="-Y,Z;"███" AND RND<RND
 153 PRINT AT CODE "="-Y,Z;"▟█▖" AND RND<VAL ".3"
 160 NEXT U
 170 PRINT AT INT RND,INT RND;"FUEL:50"
 300 LET U=USR VAL "17105"
 810 IF U<>VAL "1E3" THEN PRINT AT PEEK VAL "16515"+SGN PI,PEEK 16514;"▒,,~~"
 820 PRINT AT INT RND,CODE "?";"SCORE ";U
 2010 PAUSE CODE " COPY"
 2020 GOTO CODE "W"
 
   1 REM ▘▘ E:RND)5 # RETURN#C▝[R]"";# RETURN#C▝[R]"";# RETURN#C▝[R]"": TAN PPPPP
   2 LET M=INT RND
   5 PAUSE CODE " COPY"
   9 LET P=CODE "3"
  10 CLS
  11 FOR G=INT RND TO CODE "+"
  12 PRINT AT G,P;" "
  13 NEXT G
  15 LET F=CODE "▖"
  20 LET G=SGN PI
  34 LET R=CODE "?"
  36 PRINT AT 20,31;" ";AT 21,31;" ";AT R,P;
  38 LET D=USR 16514
  41 IF D THEN GOTO VAL "500"
  42 PRINT "Q";AT R+1,P;"[,,]";AT R+2,P;"▞" AND G=INT G AND INKEY$ <>"6" AND INKEY$ <>"7";"▌" AND G=INT G AND (INKEY$ ="6" OR INKEY$ ="7");"▐" AND G<>INT G
  68 LET S=R
  69 LET Q=P
  70 IF NOT P THEN GOTO CODE " IF "
  75 LET G=G+.5
 105 LET W=1+RND*12+(15 AND (G=INT G))
 110 PRINT AT 19,W;"▐▒▌";AT 20,W;"▖[O]▗";AT 21,W;"▛[▒]▜"
 111 LET P=P+(INKEY$ ="8" AND P<31)-(INKEY$ ="5" AND P>0)
 112 LET R=R+(INKEY$ ="6" AND R<17)-(INKEY$ ="7" AND R>0)
 115 PRINT AT S,Q;" ";AT S+1,Q;" ";AT S+2,Q;" "
 120 SCROLL
 122 SCROLL
 130 GOTO 36
 250 LET V=(100-INT G) AND G<100
 255 PRINT AT R+CODE "▝",P;"▟";AT P,P;"** CONGRATULATIONS ** "
 260 IF V>M THEN LET M=V
 262 PRINT "█[S][C][O][R][E][:]";V;"       "
 264 PRINT "               "
 270 PRINT "█[H][I][G][H]█[S][C][O][R][E][:]";M;"  "
 290 GOTO PI
 500 SCROLL
 501 PRINT AT R,P;"▒[S]";TAB P;"[▒][P]";TAB P;"▒[L]";TAB P;"▗[A]";TAB P;"▖[T]";AT INT RND,INT RND;
 510 LET V=INT RND
 520 GOTO VAL "262"
 990 SAVE "CROS[S]"
 992 PRINT AT CODE "~~",INT RND;"█[F][R][E][E][W][A][Y]█[C][R][O][S][S][I][N][G]█"
 1000 LET M=INT RND
 1010 LET P=CODE "3"
 1100 GOTO VAL "11"
 
   1 REM E:RND#▞ TAN    O[J]M[~~]RNDWM[,,]RND   7# RETURN COS FFY COPYM[,,]RND# RETURN COS 7)5 [J]M[,,]RNDXM[~~]RND[R] GOSUB ## RETURN COS [J]WM[~~]RND;;# RETURN COS [J]M["]RND▘  TAN ;>3#>=8(?▘3 VAL LN  PRINT ▒# LPRINT PI REM UEXP RND5[,,]RND▚MEXP RNDUINT RND5[~~]RND▚MINT RNDLN  RAND RNDTAN E£RND7- UEXP RND#;)5  GOSUB #UINT RNDW#;( CLEAR##TAN LN  LPRINT RND6SQR RND RETURN ""Q▒TAN P# ▌[0]  REM 1UEXP RND5[,,]RND[-]MEXP RNDUINT RND5[~~]RND[-]MINT RNDLN  RAND RND#[$]RND1111Y=MINT RNDLN  RAND RND[R]COS Y▘MINT RND▘ ▘TAN Y2MEXP RNDLN  RAND RND[R]COS Y▘MEXP RND▘ ▘TAN Y▘MEXP RNDLN  RAND RND[R]COS Y2MEXP RND▘ ▘TAN Y▘MINT RNDLN  RAND RND[R]COS Y=MINT RND▘ ▘TAN 1█11ESQR RND# RETURN[,,]ASN #INKEY$  RETURN[(]ASN #INKEY$  RETURN[~~]ASN #INKEY$ ##INKEY$ LN [-]INKEY$ # RETURN▘COS Q▒TAN 1LN ##LN [7]#TAN [)][(]1# ▞[6]  REM 2UORND NEW▘C▝Y COPY#U[,,]RND[R]C,,[J]M[,,]RND#M[~~]RNDTAN M[~~]RND#M[,,]RNDTAN 22222225ABS RND#[R]COS O#UORND#- 5▘ #▞▒ACS ZK▘;( RAND # RETURN▘SQR #COS INKEY$ 222222LN =INKEY$ #[L]""LN  LIST INKEY$ ▘  TAN 22ESQR RND#▘▘▘ RETURN[,,]COS  RETURN[~~]COS  RETURN[(]COS  RETURN[)]COS ▘  TAN 22UPEEK RND RETURN64(USTR$ RNDWMSTR$ RND RETURN+**Y▘MSTR$ RNDTAN USTR$ RNDXMSTR$ RND""Y=MSTR$ RNDTAN 22LN CHR$ RND#[R]INKEY$ LN [V]▝▘  # RETURN TO 4># RETURN RUN 4▌:5TAN    RETURN LOAD "":6TAN    RETURN LOAD 4,,# RETURN LOAD "":7TAN    RETURN RUN ""# RETURN LOAD "":8TAN   3LN #PI#[R]C▀MPEEK RNDUPEEK RND▞ #TAN UPEEK RND RETURN84(UUSR RNDWMUSR RND RETURN3**Y▘MUSR RNDTAN  RETURN54:UUSR RNDXMUSR RND""Y2MUSR RNDTAN #RNDPI)[Y]INKEY$ ▘▝ LN #"AT ▖# RETURN+ AND  OR RNDTAN 4E£RND7- UUSR RND#;)5  GOSUB #USTR$ RNDW#;( CLEAR##TAN LN [8]PILN [P]PILN  POKE PI[R]""Q█TAN 4LN Q#LN ?#C▖▘  TAN LN /PI##[R]C GOTO ▘▘▘TAN ▞▝:▞VAL LN [V]▝AT £4 SAVE ( POKE TAN 45ABS RNDQ[Z]7Q87Q?7Q?LN COS INKEY$ TAN ▘  COPYLN ##CY▘ ▘LN ##CQ▘ COPY LN ##CI▘▘ LN ##CA▘  TAN EEXP RND FAST#[,,]##█#6EXP RNDVAL LN  RAND RNDAT  LPRINT 6EXP RND RETURN[,,]COS  RETURN[~~]COS  RETURN[(]COS  RETURN[)]TAN  GOSUB #[,,]RNDTAN LN 2##[L]COS LN BPI#[L]4£LN CINKEY$ #[L]C*LN E#/ REM LN [G]INKEY$ #[L]C STEP LN WINKEY$ #[L]4 OR ▘▘▘TAN LN ###[L]4 SCROLL/ NEXT 
   2 GOTO EXP PI
   3 SAVE "RAT[S]"
  60 PRINT ,," SPEED? (1 TO 250)"
  80 INPUT U
  82 POKE VAL "17209",U
  85 CLS
  90 PRINT "[(][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,][,,]"
 130 PRINT AT CODE "+",SGN PI;"[~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][~~][)]"
 500 LET U=USR VAL "16999"
 510 PRINT AT INT RND,INT RND;"YOU" AND U;"I" AND NOT U;" WIN "
 520 RUN 
 
   1 REM ▜RND########################################(6 >"[<]:(▞+VAL $LN  PRINT ▒AT Y█NOT ( PRINT $4 LIST LN  PRINT ▒Y0NOT NOT NOT Y COPYM[L]RND5[E]RND6▙RNDE£RND)1 ; FOR 5▜RND▞=#7#7 FAST##)) ;## LPRINT ( LIST E[K]RNDY▘[W]K▒▘#  GOSUB PI6[K]RND#VAL LN [V]▝AT ( RAND ACS #C###8C#LN [X]▛#5[G]RNDCHR$ 5S# RETURN▖K#▞ #,,#- E▜RND:)[B] GOSUB PI;# RETURN█CA RETURN▒C6 RETURN▞C2 RETURN[$]C▝/# FASTE£RND777# RETURN94~~Y[-]M[L]RNDQ0F/ LET O LPRINT  FASTE▙RND#7#Y█>)[F]RND##FF▘A  GOSUB [S] LPRINT 6▜RNDE▜RND FAST5▜RND77Y▒ GOSUB #▙RND[B] FAST GOSUB PI LPRINT  PRINT #7#7 LET C▀>/ LIST Y▞> LPRINT QO▘#▘E£RND,,FY[$] GOSUB [T]7 LLIST  DIM INKEY$ )) ;# RETURN█C~~ RETURN▒CD RETURN▞C;/▝Q[$][B] GOSUB #Q█ FASTVAL ▘▜RNDE▙RND[B] GOSUB PIAT  LPRINT COS /LN  FASTE▙RNDFF6▙RND LPRINT /<>[B] GOSUB #/[W]E▜RNDUORND***[H] RETURN S< NEW?E£RND)▌ ;#▞ ,,# RETURN▞Q[$]COS # POKE RND
   9 CLS
  10 RAND USR 16562
  11 CLS
  12 PRINT "GO AGAIN ?  Y/N"
  13 INPUT Y$
  14 IF Y$="N" THEN STOP
  15 GOTO 9
  20 SAVE "SNAK[E]"
  30 GOTO 9

Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.

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Archived Media Downloadable TS 1000 Timex Computer Corporation Game

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