On Mon, Dec 31, 2018 at 1:09 AM Jim Brain <brain@jbrain.com> wrote: > > Is the goal to get a period-correct IC? Or, is it just to replicate the > 6550 functionality? I designed adapters to use 2114 in place of the 6550, so my only goal would be having the real ones. The 2001 is currently running with my RAM/ROM replacement board as two 6540 are also missing and the replacements have been lost by italian post service it seems. > > BTW, if there a handy datasheet for the 6550? Was it available mask > selectable for various combinations of select lines? I've never seen a datasheet of the 6550. I believe the various CS pins have fixed polarity. Also, I've never seen any hint on the part number printed on the case that there might be a different option. I have made a test setup that tells me how a 6550 is working or not, including when it stops obeying to one or more CS lines, so for example I can use that chip in the video RAM socket of a 2001, where it's always selected on high part of phi-2. I have such a 6550 on my 2001 video RAM and it's working fine. FrankReceived on 2018-12-31 10:00:07
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