--- John Wilson <wilson_at_dbit.dbit.com> wrote:
> On Wed, Feb 16, 2000 at 06:44:14PM +0000, Tony Duell wrote:
> > Hmmm.. I've tried to learn morse several times, and failed every single
> > time. I don't know why, but it just doesn't seem to 'click' with me.
>
> Well, having an actual use for it makes it a lot easier to remember. My
> best friend and I learned Morse code in 6th grade so that we could pass
> notes in class that no one could understand. Naturally that later fizzled,
> the 7th grade teacher was a ham and the 8th grade teacher was a radio
> operator in the Norwegian underground in WW2, so much for that idea!
My younger brother did that as a kid, too. The teacher tapped back "cut it
out" when they tried it during a test.
> I *always* wanted to do that, I actually bought a DUP11 years ago for this
> purpose but never dug up documentation on it until recently. You'd need to
> build some kind of external clock (PLL really I guess) that synchronized to
> the bit transitions of AX.25, shouldn't be a very big deal though.
My knowledge of sync serial comes from years of working with third party
devices on DEC equipment, but here goes... If the DUP-11 has a COM5025
serial chip on it then what it's expecting is something like a "standard"
bit-rate on its input connector. With the right cable, I'd expect to
feed it clocking through pins 15 and 17 on a DB-25 at EIA levels (+/- 12VDC).
We used to have racks of "modem eliminators" that were effectively null-modem
devices that would provide clocks to DTE equipment on both sides. There were
typically various options to set as well, bit rate being chief among them.
Most of ours were set to between 9600 and 56Kbps with a couple set to 64kpbs
and one to 128kbps for reproducing environments of our European customers.
Sync serial has no start bits, no stop bits, just bits. With protocols like
SDLC, there's a "flag byte" of 0x7E (0111 1110) that the receiving hardware
uses to determine the start and stop of a packet. One efficiency of sync
hardware is you aren't trasmitting 10 bits to communicate 8. The downside
is extra hardware on both ends and slightly more expensive cables to send
it all.
If I'm confusing the DUP-11 with other DEC cards that use the COM5025, sorry.
The original Software Results Corp. COMBOARD used that chip because it was
identical to whatever Qbus card we used to use when we were shipping the
HASPBOX (a PDP-11 with sync serial and a DPV-11 to communicate via parallel
to a PDP-11/70 or VAX-11/7xx).
> Stupid question: what comes out of the other side of a ham TNC these days?
> It used to be Bell 202 modem tones at 1200 baud HDX, over an FM voice signal,
> it *can't* still be that easy though can it?
In the 2 meter band in the U.S., at least, Hams are restricted to 1200 baud.
AFAIK, it is that simple. There are "pocket TNCs" that are little more than
audio modulator circuits that depend on the CPU in your PeeCee to produce
a valid AX.25 bitstream. I've seen it work with an HP-95LX - "pocket packet".
-ethan
=====
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Received on Wed Feb 16 2000 - 18:31:51 GMT