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Digivision

My first introduction to the world of SSTV was rather an indirect one. When Robot Research Inc released the Robot 1200C scan converter in 1984, one of the first UK recipients was Jeremy Royle, G3NOX. The Robot had (has) the ability to save and load pictures via a parallel IO port for connection to a computer. The computer of the day in the UK was the BBC micro and Jeremy, knowing that I was a keen Beeb programmer, asked if I could write some software to transfer pictures between the Robot 1200C and the BBC micro. At the time, I wrote all my software using BBC BASIC, and as this wasn’t fast enough to cope with image transfers, my first step was to learn 6502 assembly language. This was to come in very handy later; see the ColourStore 2000 page.

We also had to organise an interface between the Beeb and the Robot. The Robot has separate 8-bit input and output ports (on one connector), with two handshaking lines for each. I decided to use the “User Port” on the Beeb for input and the parallel printer port for output. The timing diagram of the Robot seemed quite stringent and I felt that an interface to latch the data from the Robot before passing it to the Beeb’s User Port would be necessary. I remember that Jeremy went straight to the top, contacting a friend at the BBC for assistance! I still have the hand-drawn circuit which was used in the finished interface, and it all worked very well indeed.

The Robot 1200C scan converter

The Digivision software stored pictures from the Robot 1200C on floppy disks. Jeremy, ever the pioneer and never afraid to spend a few pounds on a worthwhile project, bought one of the early “Winchester” disks on which to store his pictures. I believe the capacity was a massive 20MB! As far as I recall, he was the only Digivision user to use one of those early hard drives for storage - everyone else just used 5.25” floppy disks. Despite this limitation, the system was quite popular and at least a dozen were in use in the UK. I have no records from that era, but some users of the system included G3NOX, G3CDK, G4UKL, G1LXI, G0BDD, G0BXJ and G8SLB. If anyone remembers who the other users were, please let me know.

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