On Mon, 7 May 2001 at 22:46:18, you wrote:
(ref: <[EMAIL PROTECTED]>)
>> You could try copy <filename> ser2 (or ser1) but at a slow baud rate to
>> avoid problems. When we first developed QL Terminal (in 1988) we found
>> 2400 was the maximum safe rate, and even then sometimes chrs were lost.
>> The main problem was input to QL.
>
>When developing a terminal emulator to connect to my college computer
>system (around 87/88), we encountered major problems on the input side
>if the rate was too high: the buffer in the 2nd processor would
>over-run, causing an 11 (if eyes remembers correctly) character delay -
>nothing would appear from the SER port and then as each further
>character was received, we'd get the 11th previous character (with no
>loss); the only cure [we found] being a RESET. We generally used 1200.
..... but _not_ the reset button - the resultant system reset does not
get through to the 8049. The only cure is a power down.
>
>I still use the emulator that was written to connect my QL to my other
>PC (486, running Dos+Windoze 3.1/FreeBSD Unix) and I find 1200 baud is
>the best rate I can manage.
It is all down to handshaking and how fast the QL can accept and process
the data. If the QL invoked the handshake line, and DTR was connected
to RTS, then it was possible to get 9600 successfully - especially with
Gold Card/Super Gold card. The Astracom modem succeeded by buffering
the data and feeding it to the QL more evenly, and always reacting
correctly to handshake. At the time it was the only non-specific QL
modem designed to cope with the QL serial input.
The buffer-overrun happened if QL DTR (really an RTS in this use) was
connected to remote DTR (ie printer lead), or if the 8049 failed to set
DTR (if correct cable used). This happened very easily, as the 8049
code was bugged. For instance if it was making a sound, it 'forgot' to
to much else.
Even the Astracom could not cope with this.
This discussion is a classic example of how even the basic QL problems
keep re-surfacing. This issue was fully understood and solved in 1988
(if I recall correctly) with Hermes - a replacement 8049.
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