Hey guys. I'm Paul, and I just joined the list. Right now I'm working on
a new 2600 tester cart. I thought the original diagnostics was just about
useless, so I decided to make a better one. My cart uses the Stellar Track
text engine for most of its display.
I've also recently built a 100 game multicart with an onscreen menu system
also using Stellar Track kernal. I'm working on a way to mass produce the
circuitry required. Currently I've only made one because it took about 6
hours to hand wire and solder the circuit and cram it in a cartridge.
My question: does anyone know how long you need to wait to read the
keyboard controllers? The guide states 400 microseconds. See if my
thinking is sound: A processor running at 1MHz eats a cycle once every
microsecond. So since the Atari runs at 1.3MHz, a cycle lasts a little
less than a microsecond. So I need to wait a little more than 400
cycles. About 530 or so. My testing seems to confirm this, but I wanted
to double check. The Colecovision with the Atari adapter was the most
finicky about the delay being long enough.
Some ideas:
The Commodore 64 Programmer's Reference Guide is an excellent 650x
reference. Tells you EVERYTHING you would ever need to know. Has a
detailed list of all instructions with OP CODEs, addressing, no. of cycles
used, etc. These books are for sale on ebay all the time.
About paddles. This method worked best for me:
LDA INPT0 ;3 cycles
BMI charged1 ;2 or 3 cycles
DEC Pot1 ;5 cycles = 6 or 10 cycles
charged1
This was also suggested as a method of reading the paddles:
lda INPT0 ;3 cycles
asl ;2 cycles
adc Pot1 ;3 cycles
sta Pot1 ;3 cycles = 11 cycles
But I found that although only bit 7 in INPTx is documented as used, you
can't assume that the unused bits are zero. So you have to make it:
lda INPT0 ;3 cycles
and #%10000000 ;2 cycles
asl ;2 cycles
adc Pot1 ;3 cycles
sta Pot1 ;3 cycles = 13 cycles
-Paul
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