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

Paul Berger phb.hfx at
Thu Jun 18 07:20:44 CDT 2020

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.


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