On 10/14/2016 12:48 PM, smf wrote: > On 14/10/2016 11:35, Gerrit Heitsch wrote: >> And don't forget, the DRAM controller came later, the 6566 was SRAM, >> so it had to fit into whatever space they could find. That also >> explains the weird multiplex address pinout. > > I need to track down who told me they had a decap of the 6566 and it > looked like it was based on the dram design with traces cut. VIC2 was > originally destined for a dram system, circumstances meant the 6566 was > first out of the gate & that the p500 (the target machine) never went > into full scale production. Well, MOS usually counted upwards so the number suggests that the 6566 came first. > > 6567 do multiplexed for dram and non-multiplexed for character rom, I > would guess that has just as much to do with any weird pinout. TED is completly non-multiplexed. It's likely the number of pins they had and non-multiplexed just didn't fit into a 40pin. The VIC in the VIC-20 was SRAM and had the same address space and 12 data bits. The problem is, for DRAM you also need /RAS and /CAS which means 2 more pins. Going to multiplexed addresses solves that problem. But then you need to demultiplex for the char ROM. The easiest way to solve that is to have some non-multiplexed addresses and the 74LS373 as used in the C64. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2016-10-14 11:03:14
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