Am Freitag, 7. Februar 2020, 22:15:29 CET schrieb Spiro Trikaliotis: > Hello, > > just my 2 cents worth of guesswork: > > * On Fri, Feb 07, 2020 at 09:20:29PM +0100 silverdr_at_wfmh.org.pl wrote: > > Mapping says about D6510 ($00): > > > > On power-up, this register is > > set to 239 ($EF), which indicates that all bits, except for Bit 4 > > (which senses the cassette switch), are set up for Output. > > As $EF only has bit 7 unset, this sentence does not make sense. ;) > > > The KERNAL initializes the DDR to $E7 and the Data register to $2F. > > On RESET, I expect the CPU to make sure that the DDR has all (available) > IO as inputs. This way, the C64 ensures that the "hard-coded" memory > configuration is active on power up. And that's the only "defensive" way > to ensure that there are not two sources (CPU and external device) > driving a data port. > > So, all "connected" I/O port bits should be input. For the non-existing > ones, I do not know. > > The Data register is not important here, and I would not wonder if it > would either be uninitialized on RESET, or if it would get exactly > what was received as input on RESET. > > For the used bits of the DDR, I am sure - especially since regardless > what you store into $00 and $01, a hard reset "re-animates" the C64, and > because this is the only way this can be done without the risk of two > devices driving a line. "DDR and DATA are both initialized to 0 on powerup/reset. on the C64 pullup resistors are installed on bits 0,1,2,4 which gives the inital standard memory configuration." see https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/CPU/cpuport/ -- http://hitmen.eu http://ar.pokefinder.org http://vice-emu.sourceforge.net http://magicdisk.untergrund.net Wenn man das Jungsein mit dem Hoeren von so ner Affenmucke bezahlen muss bin ich lieber alt. <Jihad/Hitmen>Received on 2020-05-30 00:51:30
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