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From: terry@uts.amdahl.com (Lewis T. Flynn)
Newsgroups: comp.lang.asm370
Subject: Re: 3270
Message-ID: <51Tl01IP77Us00@amdahl.uts.amdahl.com>
Date: 20 May 91 18:07:38 GMT
References: <9105160748.AA14752@ucbvax.Berkeley.EDU>
Reply-To: terry@amdahl.uts.amdahl.com (Lewis T. Flynn)
Distribution: inet
Organization: Amdahl Corporation, Sunnyvale CA
Lines: 41

In article <9105160748.AA14752@ucbvax.Berkeley.EDU> IBM 370 Assembly Programming Discussion List <ASM370@OHSTVMA.BITNET> writes:
>
>             Can anyone tell me what should I do to write an
>             IBM 3270 emulation on PC ? Which manuals must I have ?

The single most important manual is the 3174 control unit manual. I'd
be more explicit as to title, order number, etc., but I don't have one
handy. The KWIC index should be able to help there though. It has all
the various sequences you will need to handle as well as describing the
various choices for connecting.

In general, though, I'd advise you to think twice about this. In order
to connect as a 3270 to a system, you will need some hardware either an
IRMA card equivalent for local connection or an sdlc/bisynch card for
"remote" (remote by 3270 definition). Then you'll have to do all the
esoteric programming necessary to look like a control unit in that
environment and only then can you write the terminal code. I guess
you could use a token ring card and go in through a 3174, but I know
less about that interface. The 3174 manual should cover it, though.

If you don't need any of these things, then you're dealing with a case
where someone has already done most of the hard work and you need to
investigate it more fully. Most existing emulations are one of five
types: a hardware card that makes the PC look like a 3278 (or whatever)
to the 3[12]74; a similar arrangement except the PC looks like a remote
control unit and in connected to the front end box (a 3745 or something);
the PC connects to a box (either by ascii async or by local net) which
in turn looks like a 3174 to the host (either by channel attachment or
as a remote); and the PC connects to the host by whatever means and
software in the host does the conversion there. 

A possible addition to these is tn3270 emulation. It's my understanding
that there is some knowledge on the host side (which would lump it
under the fourth category), but I could be completely wrong. If you're
unfamiliar with this, it's a form of telnet except the session appears
as a 3270 to the application.

This is all a bit vaguer than I'd like, but it's been a while since I
did any of this.

Terry