[Coco] Preserving old CoCo diskettes...

[Gene Heskett]

On Tuesday 18 May 2010, Roger Taylor wrote:
>At 11:04 PM 5/17/2010, you wrote:
>>I, and Robert Gould, have spent quite a bit of time with this over the
>> last year or so, and I have come to the conclusion that the SC6551 is a
>> drain bamaged chip and that the only real cure is a different uart. 
>> However, at 4800 baud, where no flow controls are needed, its as bullet
>> proof as any.
>
>The UM6551 can handle 230400 bps with a 3.6864 mhz crystal as long as
>the CoCo uses tight code and can keep up.
>
Does it handle DTR/RTS/CTS etc differently from the SC6551?  Or am I wiring 
my null modem cables incorrectly?  The problem is that sc5551.dr has no tx 
buffer, only rx.  The only way to stop incoming data from this machine is to 
stop the transmitter which drops the CTS line, stopping this machine.

Unforch, if an rz originated ack byte arrives to be sent during this time, 
since there is no tx ring buffer, the tx chain is frozen and rz is put to 
sleep by the sc6551.dr.   Boom, full rx buffer and rz is sleeping and cannot 
empty the buffer which would re-enable the 7 wire protocol.

The older aciapak.dr had buffers going both ways and did NOT have this 
problem.

-- 
Cheers, Gene
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