[HECnet] DDCMP sync?

Peter Lothberg roll at stupi.com
Mon Jan 25 19:54:22 CST 2021

If you want to go reasonable fast, most common is v.35 and rs422,
data and clock are the same differential signals but status signals
are different.

Most (old fashion out of date) T1/E1 CSU/DSU's have v.35..

Thanks for your great job with the PY router!


----- Original Message -----
> From: "Paul Koning" <paulkoning at comcast.net>
> To: "hecnet" <hecnet at Update.UU.SE>, cctalk at classiccmp.org
> Sent: Monday, January 25, 2021 8:46:21 PM
> Subject: [HECnet] DDCMP sync?

> In playing with DECnet I built a DDCMP implementation which deals with a byte
> stream, normally from a UART.  So that works nicely with async link DDCMP as
> found in RSX and several other operating systems.  But the speed is limited.
> The other option would be synchronous links, which would enable connections to
> DMC11 or the like at speeds up to 1 Mb/s.  But synchronous comm devices that
> connect to modern computers aren't so easy to find, though I have seen a few.
> After playing with Arduino for LK201 keyboard emulation I started to wonder if
> one could be made to be a synchronous comm link with a USB back end, with low
> level things like byte framing and maybe DDCMP packet format handling in there,
> but the protocol state machine in the host behind the USB interface.  For
> moderate speeds that seems entirely practical.  For 1 Mb/s, probably not,
> though perhaps one of the fast ARM based units with its built-in SPI could be
> warped into that.
> The alternative would be something like a BeagleBone Black (or Green) such as
> David Gesswein used as the engine for his MFM hard disk emulator.  That clearly
> could do the job without any strain.
> So I'm wondering: would there be interest in such a thing?  If yes, should it be
> a modem-connected one (RS232 signaling, bit clock supplied externally by a
> modem or modem-eliminator)?  Or should it be the "integral modem" short
> distance type, the ones that used a pair of coax with 4-pin AMP connectors like
> this
> https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/206060-1/15588
> ?
> 	paul

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