I didn't think of TN3270 as an intermediate step so far. I cannot really assess how much value that brings for the end goal, though it might be at least fun and educational. Thanks for the insights, especially 3270.pdf seems very interesting.
On Tue, Jan 14, 2020 at 07:23:55AM -0800, Charles Mills wrote: > Would talking the TN3270 protocol to a 3270 emulator do the job for you? > That solves all of the hardware issues: it is simply TCP out of your > implementation and into the emulator. > > You could then if you wished "graduate" to a real 3270 terminal. If I were > doing it I would go SNA but that is because once upon a time I knew SNA at > the bit level, but little about how bus & tag worked at that level. > > I can't speak much to physical connection or the layer immediately above > that but this book http://ruelgnoj.co.uk/3270/3270.pdf is the bible of the > byte stream going to the device. > > There is no real reason you could not drive one from Linux or Windows. A > Raspberry Pi with a 3270 attached would be an amusing idea. > > BTW, RS232 is a specification for the plug between a device and a modem. It > is at a lower level in the stack than most of the other things you mention. > Yes, it would be relevant to a dial-up SNA implementation. The "bits going > over the modem" layer of SNA is called SDLC > (https://en.wikipedia.org/wiki/Synchronous_Data_Link_Control). > > Good luck! Sounds like fun. > > Charles > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On > Behalf Of Alexander Huemer > Sent: Tuesday, January 14, 2020 1:52 AM > To: IBM-MAIN@LISTSERV.UA.EDU > Subject: Talking to 3270 terminals? > > Hi > > I am new to this list and would like to discuss an idea and ask several > questions. > > * Did anybody ever attempt to 'talk' to 3270 terminals with something > different than an IBM mainframe? > > This might sound like a strange idea, though I find it intriguing to be > able to display content on such a terminal and be able to receive > keyboard input from it. > > I guess the most straight-forward way to attempt something like that is > to use a 3270 terminal attached to a 3174 or similar and try to talk to > that instead of the terminal itself. I wouldn't know how to interface > with the terminal directly over the coax. > > * What's the best available documentation regarding 3174 models and > their features? > > I poked around on ibm.com and google but wasn't able to find much. It > seems like there were several different physical-layer north-bound > interfaces for 3174. Bus&Tag, Token Ring, Ethernet, RS232 (if I am not > mistaken, for dial-up connections), maybe others? > > Bus&Tag doesn't seem to be a good candidate, it's difficult to interface > with as far as I understand. > Ethernet is way more common these days than Token Ring, though TR NICs > are easy to procure second hand and protocol support under Linux (the OS > I am most savvy with) is in place. > RS232 is easy to interface with also, though then again, I am not sure > if that interface really exists. > > * Did the LAN interfaces (Ethernet, TR) talk SNA on layers 2 and 3 or > was there by any chance something going on with TCP/IP? I doubt it > though. > > Talking SNA with custom software doesn't seem to be a low-hanging fruit. > From where I stand right now I cannot say how straight-forward the > network traffic between the mainframe and a 3174 is, how difficult it > would be to emulate that protocol with custom software over several > layers. > > * Is anybody on the list here able to provide protocol traces from the > link between mainframe and 3174 over any interface? pcap format is > preferred, though anything would be valuable. > > I would appreciate any thoughts regarding this topic, especially to the > questions marked with asterisks. > Also, if anything is known regarding a similar thing with 5250 instead > of 3170 terminals, that would be interesting as well. > > -Alex > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
