Hi All,
I’ve been looking at the Asteroids script that’s on the TT FTP lately and am a bit puzzled as to why part of it won’t work!
I’m talking about the one that has tests for RAM, ROM, draws the cross on the screen, triggers the sounds and checks the address decoding using the probe.
It’s this last test that I seem to have a problem with!
I’ve done it on a sick board and all the chip selects check out perfectly except for the one for PROM2 (L3-7). This one always reads 0 on the probe. Just to be sure I’ve tried the same on a working board but I get the same thing.
Now thing is, I’ve gone over the schematics and checked the pin numbers and memory addresses, together with checking over the script and I can’t really see much of a reason why just this one would not read correctly when all the others do.
Before I scratch my head much more, as this script has been out there for over 4 years now has anyone else resolved this? I must be missing some very obvious point I guess?
>From what I can make out the script just reads from the given address 64 times and with the probe set to sync to the address cycle counts the number of times the chip select is pulsed (or goes low rather). It then takes the result from the probe tip, AND’s it with 7F and sees if the probe registered all 64 hits. I think :o)
Anyone explain what’s going on?
Ta,
Martin.
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