[net.micro] hacking the zx-81 rom

prindle@nadc.arpa (03/29/83)

Here are two not-too-useful programs which do things that Uncle Clive would 
rather we didn't know we could do.  They do open some interesting possibilities
though:

Program #1: "HOW MANY COLUMNS DID YOU SAY?"  (definitely not for 1K)

 10 DIM A$(818)
 20 FAST
 25 LET A$(1)=CHR$ 118
 30 FOR I=2 TO 817
 40 LET A$(I)="F"
 50 NEXT I
 60 LET X=PEEK 16396
 70 LET Y=PEEK 16397
 80 POKE 16396,(PEEK 16400)+6
 90 POKE 16397,PEEK 16401
100 SLOW
110 IF CODE INKEY$=0 THEN GOTO 110
115 FAST
120 POKE 16396,X
130 POKE 16397,Y
140 SLOW


Program #2: "16 CHARACTER SETS?" (for 1K or 2K, use 17300 instead of 30000 etc.)

 10 PRINT AT 10,10; "HERE WE GO"
 20 POKE 30000,62
 30 POKE 30002,237
 40 POKE 30003,71
 50 POKE 30004,201
 60 FOR B=0 TO 30 STEP 2
 70 POKE 30001,B
 80 FOR I=1 TO 20
 90 NEXT I
100 RAND USR 30000
110 NEXT B


Now to pay: Does anyone know if it is possible to display more than 64
different characters (and their inverses) at the same time (presuming additional
ROM with real characters); or, more complexly stated, does anyone know
the exact mechanism by which the bytes corresponding to the character
patterns are read by the custom logic chip and how these are made to correspond
to the codes in the display file???  Or perhaps I should ask "is anyone Clive
Sinclair?".

I am not on info-micro, so please send any insights to me or info-zx.

					Thanks,
					Frank Prindle
					Prindle@NADC