

No, the 6551A is able to operate in a 2 MHz system, the 6551 can only
take 1 MHz without problems.

If you see a 8551 made by MOS or CSG, take it, its a 6551A.


I know no fixed version of the 6551. There are different possibilities
to work around this bug. The easiest is to tie _CTS to GND and
use _DSR or _DCD as _CTS. It should be easy to fix the software,
_DSR is bit 6 and DCD ist bit 5 of the Status Register (Read 6551
with RS1 = low and RS0 = high).

Using the _CTS-line can lead into big trouble. The 6551 _instantly_
stops transmission if _CTS goes high. This means, that you may
get only a half byte...

Gerrit
