2K bytes of CMOS static RAM are addressable via the I/O ports
resident on the stereo sound generators. A re-chargeable
battery can be included to power the RAM during shut-down,
hence, the RAM is effectively non-volatile.
The CMOS RAM chip enable line is protected against switch
on/off transients with power up/down mute circuitry to avoid
corruption during the initialisation and powering down
Two real-time clocks are laid out an the board to permit the
choice of one of to manufacturers. Both clocks are accessed
via one sound generator’s I/O ports and are powered from the
on-board battery, hence time, together with a calendar, are
constantly available to the user.
If the Mullard clock IC is used, an alarm line is brought out
to a plug and can be used to bring the system out of standby
at any required time or date.
These are the main features of the board and they all
combine together to give the Nascom user all those twiddly bits
that aren’t present on a standard Nascom.
Construction of the board is quite straight forward once you
have made sure that all the track pins are in. The board can be
built up in stages once the port I/O has been added along with
the buffering. This means that it can be used solely as a video
board or sound board, etc and the other parts added as and when
needed. All the chips are reasonably easy to get hold of. A list
of suppliers of the ‘rarer’ chips is supplied with the
documentation to make things easier. The most expensive chip is
the video chip at about £30 and to populate the complete board
costs in the region of £70 which means that to add all the above
features to your Nascom will set you back by between £95. and
£100 which can’t be bad. Some savings can be made by using a
less accurate A-D converter. The one specified costs around £8
but for most uses the less accurate version at about £2 will
Programming the board is reasonably straight forward but it
does involve sending everything through the ports. Routines to
provide easy port and chip register access are pretty essential
to make the most of the board.
All an all the board is very good and value for money it has
to be bargain of the year. The main feature that I would like to
have seen included on the board would have been some circuitry
to provide a directly useable colour output, either ready for a
colour TV or colour monitor. Bar this though, I do not think
that the board can be faulted. Well worth the money.