Steven Combs sent me a copy of the Term-80 terminal program, the Plus/4
version, which works well on the Plus/4.  I have nothing to test it on, but
was able to examine the .PRG file, and found that the author uses his own
IRQ code for handling the 6551.  So that's a case where the rom error would
never come into play because the author uses his own replacement code
instead of the rom code.  He does that by hijacking the IRQ ram vector at
$0314.

I've asked Steven to send me Plus/4 terminal software that doesn't work so
well.  Maybe we can find one that doesn't bring in new ACIA handler code,
and we can see if any errors match the expected doubling of non-null
characters that the rom error should produce.  Then if he can arrange to
flash a new eprom containg the fix, we can see if performance is improved.

Here's Steven's video on the Plus/4 6551:

https://www.youtube.com/watch?v=daoAllAv9qo

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