Posted By
Ramtop
on 2018-03-18
13:24:08
|  Re: Possible 8501 replacement kit?
I built my own 6510 board last year for testing and no disk fast loaders would work with it. Port $01 on the 6510 only has 6 I/O lines, mapped as bits 0-5. Bit 6 and 7 are not connected and unfortunately those are the bits used on the Plus/4 and C16 for serial port clock and data.
The 6510 cards on ebay reroute the serial lines to bit 5 (which isn't connected on the 8501, but is on the 6510) and the bit normally used for cassette motor control (bit 4 I think, but I may be wrong). The hacked kernel supplied with those cards patches the disk I/O routines to use the new port layout, but obviously fast loaders bang bits 6 and 7 directly and will fail to work.
From testing with my own 6510 card the only thing that is compatible with the 8501 I/O port on a hardware level (ie, when bypassing the kernel) is cassette loading. Nothing else. That's why I abandoned the 6510 and started work on a 6502 card, as 6510 boards seem to just be a semi-compatible hack. The 6502 card, when all the bugs are finally exterminated, should be pretty close to 100% compatible with the 8501.
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