IBM 3270 controller emulation

Dave Wade dave.g4ugm at
Sat Dec 9 04:38:28 CST 2017


The tn3270 support in Hercules emulates channel attached 3270's not bi-sync so may not be a good source of info. On a local 3270 controller each screen has a unique channel-controller-device address.
On a bi-sync device only the line going to the device, additional addressing is required using poll/select sequences...

The total reference book is the Datastreams Programmers Reference.

This covers most of what you want to know. Chapter 9 covers the differences encountered in a bi-sync environment.

If you need to understand the lower level bi-sync and the poll-select protocols, which I think may be what is blocking you at present try this:-

its not wonderful but it may help. Looking at the chapter on 3270's in the VM sysgen might help explain the addressing (it might not)...


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Guy
> Sotomayor Jr via cctalk
> Sent: 09 December 2017 01:38
> To: Charles Anthony < at>; General Discussion: On-
> Topic and Off-Topic Posts <cctalk at>
> Subject: Re: IBM 3270 controller emulation
> It might be worthwhile to look at the source for hercules (370, 390, z/series)
> emulator since that includes support for 3270 terminals through tn3270.  It’s
> pretty good since I can use actual 327x CUT terminals connected to a 3174
> controller which connects to hercules emulating the mainframe.
> TTFN - Guy
> > On Dec 8, 2017, at 5:22 PM, Charles Anthony via cctalk
> <cctalk at> wrote:
> >
> > I am trying to wire 3270 support into the DPS8/M emulator.
> >
> > Multics supports 3270 via a bisync connection to the 3270 controller.
> > Multics sends commands to the Front End Network processor, which
> > (originally) passed the commands down the bisync line to the 3270.
> >
> > I have a running Multics and running 3270 display emulators using
> > tn3270
> > (3270 over telnet), so I need to write the code that maps the Multics
> > commands into 3270 controller commands (and vice versa) and manages
> > the telnet connections to the 3270 display emulators and maps the
> > tn3270 traffic into 3270 controllers.
> >
> > I don't need to actually implement the bisync communications; the
> > controller emulator will be running inside the FNP emulator, but I
> > need to express controller responses to Multics in the bisync format,
> > as Multics is expecting that the responses arrived over a bisync connection.
> >
> > The problem is that I have no idea how the 3270 controllers worked;
> > I've looked through the bitsavers collection; those documents are
> > largely concerned with the displays and tend to treat the controllers
> > as 'black boxes' that just do the right thing.
> >
> > So I am seeking pointers to documentation that will give me a better
> > grasp of the controller functionality and/or discussions with someone
> > who knows how they work.....
> >
> > Thanks,
> > -- Charles

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