3 Mar
2011
3 Mar
'11
6:35 p.m.
jim s wrote:
I recall there were some 68xx parts offered to us in
the early 80s by
Motorola. They decided they didn't want to take a bloodbath on excess
quantities of rom parts which did not meet specs or were refused by the
original customer. They presented it to us as the rom was there, and you
could add the external eprom, etc. and the rom would not affect you.
That would most likely have been the MC6801 family, or the MC68HC11
family. Many of those parts had the ability to use external memory, and
optionally to disable the internal ROM.
Aside from the ROMless MC146805E2, there were few 6805-family parts that
could use external memory.
Even for the parts with an undocumented way of doing it, by applying a
supervoltage to a pin, this was only intended for engineering test and
not for production, as it stressed the I/O pad. Keeping the
supervoltage applied for an arbitrarily long time could damage the part.
At one time I wanted to develop some code for the MC68HC05F5, a variant
with a built-in DTMF decoder. There was no EPROM or OTP version of this
part. Motorola gave me documentation on the test modes of that part.
IIRC, some people also worked out how test modes worked on a few other
MC68HC05 family parts based on study of the schematics of EVB boards.
Eric