lindsay@gandalf.cs.cmu.edu (Donald Lindsay) (10/09/90)
In article <TED.90Oct8171904@kythera.nmsu.edu> ted@nmsu.edu (Ted Dunning) writes: >the worst i have seen was on an old IMSAI-8080 where FF was the trap 7 >instruction, and was also what unused memory locations effectively >contained. >if a program hit one of these instructions, the first indication of >trouble was the high order address bit blinking about once a second as >the system filled all of memory with ones over and over again. With machines of that vintage, a read from nonexistant memory would return whatever value had been on the bus, one clock before. That is, the "echo" on the bus would be sampled by the processor. On 6800-based systems, "lda b 42,x" (with a suitably awful pointer in x) would reliably return "42". -- Don D.C.Lindsay