Re: CP/M cartridge

From: Richard Atkinson (
Date: 2000-03-29 13:14:40

On Tue, 28 Mar 100 wrote:

> > Funny thing, and I don't know if anyone else has noticed this, is that
> > when I used my CP/M cartridge, I would have to try about a billion times
> > to get it to boot, but once it did boot, it would work for as long as I
> > cared to use it for (which, to be honest, wasn't ever very long since it
> > was so dang slow). Just an observation I thought I would throw in there.
> > :)
> The times I used I never had problems booting except for the fact that the 
> resetbutton did "not" work. 

Possibly the reason why the cartridge sometimes only boots after several
attempts is that the C64 has had time to warm up, hence changing its
timing slightly.

> > when the internal bus on the Z80 is in a "float" condition, the address
> > multiplexorss on the CPM cart are exposed to a voltage that is neither a "1"
> > nor a "0"
> This remark I do not understand. There are no multiplexers on the card, only 
> buffers. The Z80 itself is only tri-stated when the 6510 is active. It even is 
> not tristated when the VIC-chip is in command. In this case the buffers are 
> tri-stated. 

I think Bil means the address multiplexors inside the C64; the ones that
connect to the DRAMs. If the CP/M cartridge somehow fiddles with the
address lines at some cycle when it's not supposed to (eg. the DRAM
refresh cycles) then this could certainly cause problems. Perhaps the Z80
doesn't get tristated off the bus *quick*enough*, and this leads to
problems when the next cycle on the 6502 bus is a refresh cycle. Possibly.


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