Re: Red Alert help needed (6502 CPU question too)

At 01:35 AM 5/3/2004, Rodger Boots wrote:
>Franklin Bowen wrote:
>
>>I posted something similar on RGVAC and got no response so I though I
>>would try it here.
>>
>>The voltages on the board are perfect. The thing I can't figure out is
>>why the CPU address lines are all low! I have placed my logic probe on
>>them at power up and I never notice the high light activate or the tone
>>change. But maybe it happens too quickly for it to be noticeable? I
>>swapped the CPU with another (neither verified good) and got the same
>>results. Stable picture of garbage with no noticeable activity.
>>
>>So here is what is happening at the CPU:
>>/RESET starts low, then stays high
>>Clock in (pin 37) is 733.2 KHz. Supposed to be 1MHz according to MAME.
>
>
>MAME is wrong, probably part of why MAME says emulation is incorrect.
>
>Crystal is 12.5 MHz divided by 16 for the processor.
>
>>Clock outs both 733.2 KHz.
>>A15-A0 are all stuck low.
>>D7-D0 all pulse.
>>R/_W is high
>>SYNC is low
>>/NMI is high
>>/IRQ is low (I pulled the driving chip and tied the signal high. No change)
>>RDY is low
>
>
>Ignore my previous answer. The problem is still the RDY line being low,
>but although I can't find it on any datasheet it looks like the RDY line
>may have an internal pull-up. In any case this circuit violates every
>rule about using the RDY line.
>
>Try putting a 1 K resistor from the RDY line (pin 2) to +5 volts (pin
>8). The RDY line should then be high and the game may run then unless the
>6502 was bad in the first place.
>
>It looks like the line gets switched by the coin switch. This violates
>all DC and timing specs for the RDY input.

The crystal on my board is different, 11.7?, I think. I'll verify it later.

You were right! I tied RDY high and the board displayed something ... and
then locked up! I'll see if I can make more progress tonight or
tomorrow. I have the RA coin switch tied to JAMMA coin 1 so I wonder if RA
needs the signal inverted. The only reason I can think of tying the coin
switch to RDY is if they were missing coin drops? Hmmmm ... maybe
not. The code to catch the coin signal would still need to execute and I
don't see how pausing the processor would help that.

The /IRQ line driver baffled me. It's default is low and the only time it
goes high is if the game is running properly and /C070 gets strobed! I
still don't get that.

Thanks Rodger!

--
Franklin Bowen (Franklin@Bowen.net)
http://fmbbowen.com:39353  
---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com