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
