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Re: Use of TNC2 clones at 38400

-----Ursprüngliche Nachricht-----
Von: "Howard Long" <howard@howardlong.com>
An: <amsat-bb@AMSAT.Org>
Gesendet: Mittwoch, 31. Januar 2001 02:07
Betreff: [amsat-bb] Use of TNC2 clones at 38400

> Someone asked me a couple of days ago about what speed you'd need to run a
> TNC2 clone at to be able to get 38400bps out of it.


With TNC2 (Z80 CPU) the serial data is received in the SIO/SCC byte per byte.
The CPU has to fetch the bytes every 200 microseconds and store and process
it immediately. This is obviously the limit for 9 MHz Z80 systems.

Higher speed can be achieved using special CPU with communication controllers
as e.g. the Motorola MC68302 or 68360. These (16 Bit) machines contain a
separate SCC unit which is able to receive and store complete data packets
without intervention of the CPU!

There exists fullduplex links with 1.2 Mbit/s speed using the MC68302
in a TNC3S packet-radio controller. For 'only' 38k, there are affordable
controllers (TNC31S) available, some of them haveing 'split baud' capability
(e.g. 9600 TX upling / 38k RX downlink). Much info on that matter can be
found at http://symek.com .

73! Ulf, DK9SJ

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