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 listReceived on 2013-10-09 15:00:06
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