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

Franklin Bowen wrote:

> I posted something similar on RGVAC and got no response so I though I
> would try it here.
>
> Does anyone have a different manual than the one on-line (my board is
> about 20% different, mostly parts not populated, than this manual)?
> If so, can I borrow, buy, or get a scan of it?
> If not, does anyone have better scans of the Main Logic pages or
> schematics I can borrow/buy?
>
> 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.

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Received on Mon May 3 03:37:48 2004