80-Bus News

While reading the latest 1984 issue of this rag, i.e. June 1978, I stumbled upon an advert for the Microcode BP14C 14-slot Backplane. Succumbing to the blurb in the advert, I ordered one, pronto. A few days later, back came the goods – in a BIG box. Actually, the only thing bigger than this board is its price tag (67 quid).

To get the board to fit into my case (hand-built out of ex-county-council plywood) I had to lose one of the board slots. I tell you folks, I cried. After paying out 67 quid for the thing, here I was lopping an inch off the end with a rusty hack-saw! Now, onto the board itself. The board is of a very high standard (it should be for the price), measures 15″ by 8″ and is 2.5 mm thick. The board is covered on both sides with green solder resist (I do hear that Chris Blackmore is having one custom-built with blue solder resist to match his MAP-80 RAM board which is, so I’ve been told, really amazingly blue.....).

The sheer thickness of the board may cause a few problems to the unwary as the pins on the standard 77-way 80-BUS edge connectors just barely emerge from t’other side of the board for soldering. This fact hit me for six as the pins of the edge conectors on my old Vero motherboad were cut short so’s they wouldn’t touch anything nasty, like the mains input plug. So, after forking out all that bread buying the new motherboard I had to spend another 25 notes on five new edge connectors. After splashing out close on £100 on a new backplane with five edge connectors, guess what? My Nascom still does the odd, un-programmed action. Ah well, that’s progress, I suppose!

And now a word for all those die-hards, who, like me, intend to use the Microcode backplane with a Nascom-1.

As most owners of expanded N-1‘s know, the Nascom buffer board has a ribbon cable sticking out of its component side which connects said board to the 43-way edge connector on the N-1 board. The layout of the buffer board is such that the best way of mounting it in the system is with its component side facing the Nascom’s component side (motherboard driven from the left-hand end).

One of the main features of the Microcode backplane is that it terminates all active 80-BUS signals into balanced RC filter networks. These filter networks have to placed as far as possible from the CPU board in order to function properly, i.e. the buffer board plugs into the backplane at the end opposite the end containing the filter networks.

Now, as with most things to do with computers, it’s at this point that all the fun begins. The tracks of the Microcode backplane are laid out in such a way that when the buffer board is plugged into it, the ribbon cable on the buffer board faces AWAY from the Nascom board. To overcome this problem, I re-soldered the ribbon cable onto the solder side of the board so that it again faced the Nascom board. Owing to this piece of board surgery, the ribbon cable also needs to be twisted through 180 degrees so that the 43-way edge connector mates with the Nascom board.

Although the Microcode backplane is of a high standard and works like a dream, I don’t think it’s worth the 67 quid I paid for it. You pays yer money and yer takes yer choice .....