Autumn 1979, Issue 4

Page 8 of 30

No phone him! If you have thought of all the questions you want to ask, then if you have a pencil and paper ready, the phone call shouldn’t last more than 19 minutes, even long distance that won’t cost more than 50p, and you’ll have the satisfaction of knowing that you got the answers to the questions you asked.

Anyway, we’ll give a brief resume of what is required to expand a Nascom system. With Nascom 1, the 43 way buss connector on the back of the pcb is only capable of driving a pretty miniscule load, and so some sort of buss driver is required. All this is taken care of by the “Expansion Buffer Board”, which also includes a clock generator, and the neccessary logic to pulse the RESET line so that data in dynamic RAMS is not lost. The Buffer Board also generates (or makes use of) the additional control signals required for NASBUS which are not provided by the Nascom 1 buss connector. Note that the Expansion Buffer Board is not required with Nascom 2 as all these ‘works’ are contained on board.

The Buffer Board has to drive a ‘BUSS’, which in the case of NASBUS is 78 ways. Nascom provide two cards (known as mother boards). These are really glorified Vero boards in a non-standard Vero size. The “Mini-Mother Board” is about 4" long, and will accomodate up to 4 cards on 1" centres. The “Mother Board” is about 12" long and will accomodate up to 12 cards. For a modest system, not to be fitted in the Nascom frame, the Mini-Mother Board should be adequate.

Connection is made to the mother board using 78 way 0.1" card edge connectors, which are supplied in the buffer and memory kits.

Memory cards are available for NASBUS in 8K, 16K and 32K versions. In all cases the pcb and control logic is the same. The boards are organised in two blocks, and option links selected for different types of RAM chip. Sockets are provided for 4 2708’s, and 16 dynamic RAMS. The 8K RAM kit is supplied with 16 MK4028 (4K x 1) RAMS, the 16K with 8 MK4116 (16K x 1) and the 32K with 16 MK4116. As far as we know, these memory kits are not available without the RA chips.

If desired, the whole assembley may be mounted in a ‘standard 19"’ card frame, supplied by Nascom, but a bit of ‘DIY’ is called for, as the whole thing is very flexible in terms of layout, and careful thought is required if the frame is going to accomodate disc drives (when they appear).

We believe the disc drives will be supplied in their own case (which seems a bit silly if you have a gaping hole in your 19" frame ready for them), which will incorporate an additional power supply, as the standard 3 amp unit will be severely pushed driving discs as well. The “Disc Control Card” will mount on the NASBUS in the same way as the other cards, and is capable of driving up to four disc drives.

The I/O card (when that appears) is again -a standard NASBUS mounting card, but will be supplied with the control logic chips only. The I/O chips will not be supplied allowing you to populate the board in the fashion required.

This is an OCR’d version of the scanned page and likely contains recognition errors.

Page 8 of 30