USA model BBC micro

This is not a back-converted to UK specification model, but an original USA version BBC micro. It was sold to me ca. 2001 as being dead, and in early 2007 I finally tried to make it work. I didn't have to try hard: using a 230V PSU it just works fine... There might be an issue in the USA power supply, or perhaps it was something simple such as the keyboard cable not seated correctly when the seller (an American) tested it.

Pictured are the USA manuals (new and complete with moisture absorbing gel pack :) ). The machine itself was used but looks very clean. The keyboard has no shiny keycaps for example.

This machine has:

I've played with this machine a bit and in the process tested the disc interface, the 1MHz bus (with an Opus Challenger Disk/RAM disk), the user port (with a Morley EPROM programmer), and the composite video output using a standard PAL TV (I didn't test the RGB output as I didn't have the SCART cable with me where I tested the machine).

Testing the user port with the EPROM programmer was a bit tricky, as the USA BBC only has 20 lines of text in MODE 7 (compared to 25 on a standard BBC). This means the first few lines were missing, and other stuff muddled up due to scrolling/printing at wrong places. This means that the USA BBC isn't all that useful. One will get into lots of trouble with many programs that assume a certain amount of space on screen. This goes for graphics modes too of course. In the pictures you can see that the graphics screen uses coordinates 0-1279 (horizontal) and 0-799 (vertical) compared to 0-1279/0-1023 in the PAL models.

Additional notes 2020-7-12 (published 2020-8-18): A while ago a reader of my site who used the BBC micro in Canada/USA mentioned his micro had a way to switch between vertical resolutions via star commands, so 256 pixels (still at 60 Hz?) by issuing *UK, vs. 200 pixels at 60 Hz (vs. a normal BBC micro which has 256 vertical pixels at 50Hz refresh rate) by issuing the command *US. I didn't find those commands in the OS ROM dump that I made of the USA BBC that I once had... He mentioned that he remembers this status to be kept across a power cycle. Perhaps this was made by an add-on as normally there is no status that can be kept over a power cycle in a BBC micro that has no battery backup.

The weight of this machine is substantial, ca. 6 kg, about 1 kg more than a normal BBC micro.

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