[MRCA] [MMRCG] MSC-64 TTY project

[Ray Fantini]

Trying to keep with using period technology, have a Rolm 1602 that I was going to use and started doing a lot in assembler but between soldering and writing and troubleshooting code think I would rather solder. At first it was a simple idea, just knock the data from serial to parallel use the incoming word as a address for the ASCII word in a 2716 then convert back to serial for the terminal. But like most things the further you get along the more gets added to it.  Do have the test message generator and one UART up and running now and when we do the AA83 event this year planning on having the terminal set up churning away period style traffic for our public display so that's another potential use for this system, we had huge heavy military field phones for the public to play with this last year and that was a big hit, think this year we will have a whole nineteen eighties communications center set up for the public visitors at Fort Miles.
Did do RTTY from AA83 last year using the GRC-106 in the mutt but used a laptop for the teletype stuff so think that's cheating.

If it was not such an ordeal to work with the ROM on the 8080 in the terminal would try to pull them and read and then maybe try writing new firmware for the terminal but there are maybe six system chips that are not only soldered in but also the entire system boards have that flux or what ever it is coating  so its one thing to pull a chip when you don't mind destroying it but something else if you want to pull one and still have it work so you can make an image.

Ray F/KA3EKH

From: MMRCG at groups.io <MMRCG at groups.io> On Behalf Of W2HX via groups.io
Sent: Friday, February 5, 2021 12:10 PM
To: MMRCG at groups.io; 'MRCA' <mrca at mailman.qth.net>
Subject: Re: [MMRCG] MSC-64 TTY project


Cool project. I have some of these navy terminals (I think I got some from you!) which would be great to get working. But why not do all (most) of this in software? Get either an Arduino or raspberryPI? Then you have more control over things like sending LTRS/LTRS or LF/CR/CR for end of lines, etc. I like the elegance of doing things in hardware but maybe the flexibility of doing it in software. But cool either way.

From: MMRCG at groups.io<mailto:MMRCG at groups.io> <MMRCG at groups.io<mailto:MMRCG at groups.io>> On Behalf Of Ray Fantini
Sent: Friday, February 5, 2021 11:24 AM
To: 'MRCA' <mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>>; mmrcg at groups.io<mailto:mmrcg at groups.io>
Subject: [MMRCG] MSC-64 TTY project

With all this Covid stuff going on been spending a lot more time building things. One of the many pointless projects around here has been resurrecting an old AN/MSC-64 TACSAT terminal to be used to send and receive RTTY, couple problems with this is that they operate in 8-bit ASCII at 75 baud and Ham RTTY is 5 bit 45.5
Armed with my 1977 pdf of "73" all RTTY issue that has a good collection of digital RTTY information and my old TTL cook book started building a system to resolve these issues.
Already have built up a UART that speaks to the terminal and resolves the issues of word length and stop bits and also built up a ROM that acts as a test message generator that can be used to also playback test messages and put this all into one rack.
The next steps will be another UART that will convert the 45.5 baud 5-bit serial stream to a five-bit word that will be used to feed a ROM that will convert that five-bit word to an eight-bit word that the terminal understands.
Will need to do a little work on the translator ROM being that five bit TTY has an issue where there are not enough bits to display both letters and numbers so there is a special command in TTY that flips the print head between letters and numbers so have to recognize that command and have it shift to the numbers or letters side of the translation ROM but fortunately a lot of this work has already been done before so that old copy of 73 has been a great source of information to work all this out.
Keep in mind that I already have a fully working TTY set up using MTTY on a computer for current operations and have been using that for a while now and this exercise of building up something just using technology from the seventies and early eighties to do the same thing may be viewed pointless by some, but  I have found the process of designing, fabricating and troubleshooting to get what you have built to work very enjoyable.
I figure it will take another six months or year to get everything working correctly but it's a hell of a lot better than sitting around watching TV.

Ray F/KA3EKH

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