[MRCA] MSC-64 TTY project

[Ray Fantini]

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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