n-ramb

This was the “top” official memory board and was much advanced over the original RAM board (renamed RAM (A) after the release of RAM (B) to avoid confusion). The unit shown in the picture has additional features added, pagemode operation and switched memory protection.

By now (1980) the company was known as “the Nascom Microcomputers division of Lucas Logic Limited” and I suspect that a lot more work had been carried out following the problems with the earlier RAM board.

This board would not accept the old 4027 RAM ICs, so the capacities available were:

8 off 16k x 1 ICs type 4116 16k bytes
or 16 off 16k x 1 ICs type 4116 32k bytes
or 24 off 16k x 1 ICs type 4116 48k bytes

Addition of an optional 16k addramdaughter board gave a maximum total capacity of 64k bytes, so a single board gave all the RAM normally needed. (I think this board was produced by a third party. The circuit diagram says “PHG electronics 1982”). The board shown here would be plugged into one row of the RAM (B) board and the existing ICs from that bank relocated into the blue sockets. Additional signals were connected via a three-pin connector.

To overcome the 64k restriction of the Z80’s memory space, this board could be “paged”. Up to 4 boards could be fitted into one system and each given a different number. The boards could then switched in and out as required. A similar system is used today in all modern PCs when running in DOS modes, although the paging is carried out invisibly to the user – there is still a block size limit in force today!

ramb-upgrade

An additional facility was the block protection system. Each of the three RAM blocks on the board had a switch. This, when operated, prevented the data stored in that block from being changed. This allowed blocks of memory to simulate EPROMs (which can’t be written to normally). When the daughter board was added it became an extension of one of the existing blocks so four switches were not required.

Of course, as this board did not support EPROMs it was of more interest to the NASCOM-2 users, who already had 8 1k or 2k EPROM positions on the main board (the NASCOM-1 only had 2 x 1k positions and these were already taken by the monitor).


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