Synchronous serial Re: E-Mail Formats RE: Future of cctalk/cctech

Peter Coghlan cctalk at
Thu Jun 18 13:14:43 CDT 2020

Paul Berger wrote:
> On 2020-06-18 6:06 a.m., Peter Coghlan via cctalk wrote:
> >
> >
> > To get somewhere near back on topic, I am trying to set up a synchronous
> > serial link between two MicroVAX 3100 machines with DSH32 (or DST32 maybe)
> > interfaces.  One of the options I have is a BC19D cable and a BC19V cable
> > which seem to be identical or nearly identical.  Each plugs into a DSH32
> > at one end and has a V.24 DB25 connector at the other end.  I don't seem
> > to have anything available in the way of a pair of suitably similar modems
> > or a modem eliminator to put between the two V.24 connectors.  Can anyone
> > suggest some kind of a quick hardware hack that I could use to fill the
> > gap?  Is a pair of DB25 sockets with crossed over wiring betweeen them
> > sufficient or do I need something that generates clock signals too?
> >
> > Regards,
> > Peter Coghlan.
> >   
> >
> While I have no experience with MicroVAX, I do recall that  on the 
> machine I was involved with synchronous communications on, IBM terminals 
> and systems, there was an option for the interface to provide clocking 
> and I suppose it might be possible to set one side to provide the 
> transmit and receive clocks and cross them over to the other interface, 
> but I have never tried that.  When I worked in a development center with 
> a room full of S/38 and S/36 we had a modem rack with a large number of 
> Gandalf modem eliminators that provided clocking to the interface.
> In the field the most common setup was to have the modem provide the 
> clocks as the common carrier could synchronize them over a long distance.

Thanks for your reply Paul.  My eventual goal is to be able to use the
synchronous serial interface on a MicroVAX to connect to IBM machines that
only support bisync lines.  However, I don't have access to any such IBM kit
at the moment so I have to make do with trying to get the MicroVAX to talk
to another instance of itself for now.

As I mentioned in another reply, I have a pair of baseband synchronous modems
and were it not for a speed incompatibility between them and the MicroVAX
synchronous serial interfaces I have access to, plus another probably minor
snag, it looks very much like they would do the job when suitably jumpered.
There is even a card in the bottom of each modem case giving details of
all the jumper settings!

> Paul.

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