On Wed, 21 Feb 2001, Chandra Bajpai wrote: > > William, I'm beginning to suspect the EPROM as a problem. I'd like to rule > out > the 6502 first. I have a Radio Shack hand held logic problem - will that > work? That is fine. > I assume I check on the 6502: > - RESET Line > - CLOCK > - IRQ > - READY (What does this do?) IRQ and READY do not proveide useful information with just a probe. > I potentially could get a oscilloscope...will that be any better? Logic > Analyzer? It is better, but if you don't know what the signals look like, it is no help. > I assume there is nothing I check on the 2708 EPROM. Are 2708 still > available? They are still available. They are the same as the 2508. > I wonder if the 2708 is a drop in replacement for the 6540. There are no repalcements for the 6540, that's why the little daughter board. > I don't quite understand what you mean by replacing more than one 2K ROM. > Are you saying that the ROMS in H7 (F800-FFF) and H4 (F000-F7FF) should be > replaced > at the same time...BTW-I assume this machined worked with this ROM in place. The H7 and H4 ROM sockets are wired exactly alike. Each socket addresses the same 4K of address space. The 6540 ROMs have programable select lines. One is programmed to respond in the upper 2K and the other is programmed to respond to the lower 2K. That is why the EPROM may be causing a problem. The EPROM selects and the 6540 ROM selects may not be compatible and may be interfering with each other. A 4K 2516 EPROM would not have that problem, since there would then be only one Chip in that address space. Your daughter board may have to be modified to take the larger capacity EPROM. > FYI...so you don't get confused...I'm fortunate enought to own 2 8K Chiclet > PETs. > Unfortunately neither of them work 100%. This particular machine is > completely > dead and the other has a weird lockup problem. Try taking the ROMs from the working one and put them in the dead one. I will try to get the layout of the test connectors this weekend. The chips in the PET use more power and generate more heat than today's chips do. The RAM, ROM, CPU and I/O chips should be very warm while running. They should not be so hot that you cannot touch them. - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tml.hut.fi.
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