On 06/12/2018 05:02 PM, Mia Magnusson wrote: > Den Sun, 10 Jun 2018 14:33:41 +0200 skrev Gerrit Heitsch > <gerrit@laosinh.s.bawue.de>: >> On 06/10/2018 01:59 PM, Michał Pleban wrote: >>> Hello! >>> >>> smf wrote: >>> >>>> I assume for cost purposes they don't keep the last output value >>>> when in read mode, so when you switch back to output mode then >>>> zeros is probably the lesser of two evils. >>> >>> That might be the case when you switch from input to output, but >>> when you "switch" from output to output (i.e. you leave the >>> direction of the port unchanged, only modifying some other port) >>> it's just ridiculous. >>> >>>> Trying to replace a mos chip with an intel chip is blasphemy :-) >>> >>> Guilty as charged :-) But it's for a good reason: there are only >>> very little 6525's laying around, and if we want to make the 8088 >>> card accessible to everyone, we had to change to a chip that's >>> readily available. >> >> How about two 6522 instead? With some clever logic and mapping of the >> address bits, you might be able to come up with a register map that >> comes close to what the 6525 has, limiting the amount of change in >> the code. > > 6821's are even cheaper. Not sure if they would fit, but worth > investigating. No, register mapping doesn't work with the 6821 since you have to switch between Data register and direction register via a register bit. GerritReceived on 2018-06-12 18:03:28
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