From: MagerValp (MagerValp_at_cling.gu.se)
Date: 2005-11-28 11:05:07
>>>>> "UvB" == Ullrich von Bassewitz <firstname.lastname@example.org> writes: UvB> After lots of try&error I noticed that this piece of code UvB> prevents the driver from working. It seems as if reading register UvB> $d03f doesn't give the last value written to it. Typing in UvB> ?PEEK(53311) from BASIC proves this: It prints 255. Can this UvB> really be true? Yep. Apparently making a simple latch uses fewer transistors than a read/write register. It's a PITA, but not uncommon - e.g. the SID also has write only registers. UvB> There's a similar issue with the register bank: There's no way to UvB> read the old setting. How are subroutines or drivers supposed to UvB> work if they cannot read and save the old settings before UvB> changing anything? You have to keep a shadow register if you want to read back the value. -- ___ . . . . . + . . o _|___|_ + . + . + . Per Olofsson, arkadspelare o-o . . . o + MagerValp@cling.gu.se - + + . http://www.cling.gu.se/~cl3polof/ Message was sent through the cbm-hackers mailing list
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