93 Z disassembly - I have jsrs to non prom location.

[Mike]

>Hey,
>
>I have finished the TCC control routine, and I think I understand
>all of it, except how the TCC actually gets triggered.  

I wrote to the list on Dec. 21, 1998:

>>Try looking at the logic starting at D1C9. I suspect the TCC is controlled
here >>though I've never seen a PWM output at $4008 :)

Did you look there yet? That's where I think it is.

>There aren't
>any things checking the TCC bit and setting a register in the $1000
>range.   I did find some odd code that does jsr into the $5000 range,
>the prom is mapped from $8000-$FFFF, so $5000 would have to be
>built into the computer's internals.    

Not necessarily. Look on the ECM board and you'll see a 60-pin edge
connector. Likely GM attaches equipment to this port and maps code hooks in
the $5xxx range for testing and development etc. Closely examine the section
of code that looks at $5000 (among others) and compares the 16-bit value
there to #$7E5x. Then look in your code for opcode '7E' and you'll see it's
a JMP. The ECM checks for the presence of something attached there by
examining the program code there. If it seems valid (JMP $5800 for example),
the ECM enables the hooks. This is what I gather at least. I might be wrong.

Look around DC3E in your code, Roger, to see where the ECM checks to see if
there's something valid at the $5xxx range.

>There about 10 of these jsrs
>to different addresses in the $5000 range.  Does anyone have any
>idea what these do?   If I really want to know bad, I will setup
>a prom to read that range (while petting the watchdog), and output
>that data to the aldl port.  I am thinking some of the hardware
>operations (TCC and several others maybe) are being done there.
>

No normal hardware operations are done in these routines. They are strictly
GM development and test areas.

In most P4-style ECMs, you'll find the outputs controlled by accessing the
$3xxx registers and some registers in the $4xxx range. Some odd animals like
yours that actually have stuff mapped to $1xxx don't automatically use them
for discrete control. In the case of your TCC, I think you'll see $4008 is
the control output and they send either 100% duty to turn it on or 0% duty
to turn it off.

If you do write a PROM, try emulating the essential code at D1C9 and have it
toggle the value written to $4008 and then look at the TCC output for
activity. Don't forget to include lots of COP resets all over the place.


--
 Mike