Hi Andy, Larry and All,
I can confirm Larry's statement about the unreliability of serial port
timing under Windows 95/98. This is a consequence of the change to
pre-emptive scheduling from Windows 95 onward. The system timer (18 ticks
per second) that Andy refers to is not directly accessible under Windows and
any timings based upon it will be found to be inaccurate by a few mSec
either way. It is only correct on average.
My solution to this is to use a Comtrol Hostess i card, which come in 4, 8
or 16 RS232 port versions. The card has its own processor and memory and can
be downloaded with a program to operate the ports. The interface to Windows
is then through dual-ported memory.
John, G4CNN
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