Re: Strange 8255 behavior

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Sun, 10 Jun 2018 16:00:46 +0200 Message-ID: <23250952-d488-189e-c7ea-3854cbdf8c35@laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 06/10/2018 03:47 PM, Michał Pleban wrote:
> Gerrit Heitsch wrote:
> 
>> Might not be possible since the 6525 has NMOS output drivers which allow
>> you to do things that you can't do with CMOS output drivers. Namely
>> having 2 outputs (one LOW, one HIGH) directly connected.
> 
> The only role the 6525 has on the board is to connect to the 6526 on the
> other side to pass some signals.
> 
> So what we thought to do was rather implement *both* the 6525 and 6526
> in the CPLD, or more precisely, only these parts which are necessary for
> this particular interface. Then the CPLD would be directly connected to
> the 8088 bus on one side and 6509 bus on the other side. I don't know
> about 8088, but I have already connected a CPLD to the 6509 before and
> it worked like a charm.

Another Idea would be to use an AM2130 (datasheet is available online) 
or similiar chip instead if you can find them. That's a 1k x 8 dualport 
RAM with built in arbitration. Should be perfect to interface 2 systems.

  Gerrit