Mr. Dot Up and Running

General games-related topics
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jsweinrich
Posts: 16
Joined: Mon May 31, 2021 6:22 pm

Mr. Dot Up and Running

Post by jsweinrich »

Well, I got Mr. Dot up and running. I bought a cassette recorder off ebay and everything works great except the TV is not to happy with the RF signal. Weird that the TV finds the ZX81 at channel 86 but it is set for a cable input not antenna. Also, the video is sometimes reversed. I guess I should look into a video mod...
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Here is Mr. Dot:
10 REM Updated "Mr. Dot"
20 REM using the "Halley"
30 REM version of the ZX81
40 REM Program presets
50 REM variables, plots
60 REM a dot in center
70 REM of the screen, then
80 REM checks for JOYSTICK
90 REM movement. If there
100 REM is a JOYSTICK movement,
110 REM plots JOYSTICK
120 REM direction or unplots
130 REM if the "Action" button
140 REM has been toggled.
150 REM If either horizontal
160 REM or vertical limit
170 REM is reached the plot
180 REM or unplot location
190 REM wraps around screen.
200 REM DOT is the plot/
210 REM unplot flag.
220 REM X and Y are the X
230 REM (left-0, right-63)
240 REM and Y (bottom-0,
250 REM top-43) locations
260 REM on the screen.
270 REM JOY is the value
280 REM of the last time the
290 REM JOYSTICK was read
300 REM using peek.
310 LET UP=30
320 LET DN=29
330 LET RT=23
340 LET LT=27
350 LET UPRT=22
360 LET UPLT=26
370 LET DNRT=21
380 LET DNLT=25
390 LET ACTION=15
400 LET CNTR=31
410 LET DOT=1
420 LET X=31
430 LET Y=21
440 PLOT X,Y
450 IF DOT=0 THEN UNPLOT X,Y
460 LET JOY=PEEK 32767
470 IF JOY=CNTR THEN GOTO 440
480 IF JOY=LT OR JOY=UPLT OR JOY=DNLT THEN LET X=X-1
490 IF JOY=RT OR JOY=UPRT OR JOY=DNRT THEN LET X=X+1
500 IF JOY=DN OR JOY=DNRT OR JOY=DNLT THEN LET Y=Y-1
510 IF JOY=UP OR JOY=UPRT OR JOY=UPLT THEN LET Y=Y+1
520 IF JOY=15 THEN GOSUB 590
530 IF X<1 THEN LET X=63
540 IF Y<1 THEN LET Y=43
550 IF X>63 THEN LET X=1
560 IF Y>43 THEN lET Y=1
570 GOTO 440
580 REM Toggle ACTION button
590 IF DOT=1 THEN GOTO 620
600 IF DOT=0 THEN LET DOT=1
610 RETURN
620 LET DOT=0
630 RETURN

Here is the schematic (I just updated the schematic I made back in the 80s):
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