Re: 6530 replacement

On 10/09/2013 08:18 AM, Baltissen, GJPAA (Ruud) wrote:
> Hallo Gordon,
>
>> /OE (Pin 22) from EPROM is the inverted Phi2 (Pin 3) from 6530 (but this isn't your problem)
>
> But it will if I don't correct it. I notified the use of the inverter in the 8250LP to Gerrit too and he explained that this is needed because of the use of two 6502s in the same design. The inverted PHI2 makes sure the EPROM is only active for the right 6502.

Since that part of my reply was only in a direct email... The large 
drives use two 6502 running on the same clock speed, but 180 degrees out 
of phase (kind of like the 6510 and VIC in a C64). They use the same 
data bus while the address bus is seperate and only a certain part of 
the RAM can be seen by both CPUs.

To make that work, all chips used on that construct must have PHI2 of 
the CPU they are working with as part of their enable signal. Otherwise 
it would happen that 2 chips are active at the same time and fight over 
the data bus.

It's a simple way to make 2 CPUs work together without getting in the 
way of each other while still being able to share data.

  Gerrit



       Message was sent through the cbm-hackers mailing list