[Techtoolslist] Another midway 8080 and pod (space invaders deluxe) question

[Alex Yeckley]

> Comes back with 0xFF.  Hit loop and it starts to wander all over creation.

>From highest to lower probability, based on my experience. YMMV:

1) bus fight with ROM or I/O bus
2) bus transceiver(s) bad
3) genuine RAM problem
4) I/O control latch problem
5) incorrect clock phasing or enable signal threshold between the even and
odd RAM banks
6) other

> Any ideas on why ram would fail this way?

They reportedly could suffer physical damage if the -5V (or was it the +12V)
was not properly supplied.  Not sure the exact failure mechanism was at the
die level.

Alex
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ayeckley at elektronforge.com
www.elektronforge.com