On Thu, Feb 1, 2018 at 2:47 AM, Mia Magnusson <mia@plea.se> wrote: > Den Tue, 30 Jan 2018 23:53:46 -0500 skrev Ethan Dicks > <ethan.dicks@gmail.com>: >> On Tue, Jan 30, 2018 at 8:27 PM, Mia Magnusson <mia@plea.se> wrote: >> > I know that there are some existing projects where you put a small >> > PCB between the 6502 and the motherboard, and while that would be an >> > elegant solution, it seems historically more incorrect than adding a >> > 62256 to the expansion connector. But maybe I'll change my mind >> > later. :) >> >> That's what I'm doing for my 2001-8. I don't have enough working >> 6550s to run an 8K machine, so I have a single 62256 on a CPU socket >> board strapped for 8K. It would just take moving a jumper to go to >> 32K, but with original 6540 ROMs (the board can take a JEDEC EPROM but >> I don't have one installed right now). > > Did you remove all main RAms on the motherboard, or do you use some > other method to make it not collide with the 62256? on a 2001 board, it would collide anyway because the 74LS244 on the RAM data bus are enabled. On my PET RAM/ROM board (my own design as always) there's 74LS245 between the internal RAM/ROM, 6502 data bus and the external data bus that's enabled only when the 6502 makes access to external addresses (configurable). You could disable the original 244s on the motherboard, but that would be not so "optimal" in my opinion. I believe most commercial PET RAM/ROM replacements have a bus driver on the data bus. F Message was sent through the cbm-hackers mailing listReceived on 2018-02-01 08:00:03
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