Andrew Davie wrote:
>> lax (ptr5),y ;5 illegal opcode
AD> DASM won't let me assemble that code (lax illegal), and I don't know the
AD> byte-code for the instruction. Thomas, what assembler are you using... has
AD> it been modified to allow the above, or do you have a macro or something?
I recompiled DASM 2.12 with the new mne6502.c file
which was sent to the list in June 2000 by John Saeger.
Before that, i used macros:
opLAX_IY = $b3 ; illegal opcode for lax(),y
MAC LAX_IY
.byte opLAX_IY,{1}
ENDM
Some other lax opcodes:
opLAX = $af ; illegal opcode for lax absolute
opLAX_ZP = $a7 ; illegal opcode for lax ZP
opLAX_Y = $bf ; illegal opcode for lax,y
AD> Your mod was pretty neat, by the way (I was waiting for somebody to point
AD> out that it could be extended to multiple lines).
You also could use the table approach with different
heights for each row: (result might look funny :)
table .byte 0,0,0,1,1,2,3...
AD> However, I'm wondering at this point... have you actually tested it and
AD> confirmed it works? The timing is so tricky that any shift in timing seems
AD> to bugger the whole thing.
Yes, I've tested it, it works.
Just make sure, that you finish the last four writes to
the GRPx registers at the correct times (43,46,49,54).
Most timing problems occur due to accesses or branches
to different pages. Check the alignment of your data
and then look at the listing file of DASM and check if
you are branching across page boundaries.
BTW: The 48 pixel routine you're using isn't a real 48
pixel routine. If you try use bit 0 in your data, you
will see, that the last column of first digit displays
the data of the third digit. If you want real 48 pixels
you have to use the VDELPx version.
Have fun!
Thomas
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