osiweb.org

FYI , there are 2 different 620 schematics 1 on this site and 1 on marks osi board index, both appear to be the same at first glance but in reality are polar opposites
one would be used for 600/610 to 48 pin buss the the other would be for 5xx cpu board to use the 610 for memory and floppy control
they are dated 1 day apart and labeled receiver and transmitter the gates have been flip flopped .

Grant

Very interesting. It looks like two configurations of the same card. The "Receiver" would be the one I was aware of (and the one that was advertised), to allow the SBII to control the 48-line bus.

The "Transmitter" configuration just has all the 7417's plugged in backwards. There are jumpers to invert the R/W control on the 8T26 bidirectional buffers, and to handle asymmetric derivation of the 02-VMA signal, depending on direction. I assume that the +5 and GND rails to the 7417 banks are jumpered as well.

From the naming convention, I would suspect that the designer "identified" with the 48-pin bus, and probably just added in the ability to do the "transmitter" configuration because it was essentially free, and easy to do.

Does anyone have a 620 card? Pictures please?

Dave

Yes the Transmitter board layout does show jumpers to inverse the power on the 7417's it all makes sense now.

Good eye. In fact, comparing the two layouts, the Transmitter shows the 7417 chips reversed as well. The Receiver has all the chips aligned as expected.

No 620 card downunder sorry.

Picture of the OSI 620 board.

http://www.vintagecomputer.net/osi/600_ ... 0_1978.jpg

(Dave, you might want to grab this photo, as you don't have a photo of the 620 in the archive.)

/Jeff