On Fri, Oct 20, 2017 at 01:10:01AM +0200, groepaz@gmx.net wrote: >Am Donnerstag, 19. Oktober 2017, 22:22:44 CEST schrieben Sie: >> On 10/19/2017 10:03 PM, Mia Magnusson wrote: >> > Are we sure that the 6510 I/O port isn't accessible from external >> > hardware when the CPU is in DMA/three state mode? >> >> Yes... The address lines of the 6510 are output only, same for the R/W >> line. Also an access by the 6510 to $00 and $01 does not appear on the >> address and data bus. > >not entirely true - the address appears on the bus (remember, a write to $00/ >$01 _does_ write to the RAM also!) only the data does not. Right. On a C64 or C128 where the open address space (such as $de00-$dfff when nothing is connected to I/O1 or I/O2 on the cartridge port) acts deterministically, the writes to $00 or $01 would essentially copy the data from the previous VIC-II memory access to the RAM location 0 or 1. If I remember correctly, VICE correctly runs my program "dadb" that partially runs in the color RAM. I suppose it would also correctly emulate the writes to 0 and 1. It is also possible to read from 0 or 1 with the help of the VIC-II. I do not remember doing this myself, but an obvious solution would be to read the data using the sprite collision registers. Marko Message was sent through the cbm-hackers mailing listReceived on 2017-10-24 06:02:24
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