I have checked my notes again and the 6502.org site. The ROM in question is 901447-30. This is a 2K ROM for the test fixture for PETs without CRTC. The reset button on the test fixture toggles the reset line on the 6502. Normally, this would cause the 6502 to fetch the address at $FFFC-D and jump to it. Since the test fixture pulls A13 and A14 low, this causes the fetch address to be $9FFC-D. Therefore the ROM address MUST be $9800-9FFF. NOTE: If there is a ROM already in the PET at this address, it must be removed or it will conflict with the diagnostic ROM. The test fixture can be used on the original PETs with a slight modification to the system board. Since the original PETs did not decode addresses in the $9000 block, this must be enabled. Cut the trace between pins 4 and 5 of the 74LS21 at G4, and solder a wire from pin 4 of G4 to pin 10 of the 71154 at G2. The test fixture for PETs with a CRTC contains 2 4K ROMs, one for 40 column machines, and one for 80 column machines. A switch selects which ROM to run. I thought I had uploaded all 3 of these ROMs to zimmers.net, but I cannot find them there. I can upload them if they are not already there. wlevak_at_sdf.org SDF Public Access UNIX System - http://sdf.orgReceived on 2021-09-12 07:00:03
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