The Pluto Card.
The Pluto card is available in a number of different versions and with
various options, from the Baby Pluto to the Pluto Palette. The Pluto card I
shall concern myself with is the standard Pluto with the 8MHz option fitted.
The optional extended command ROM was not fitted. The cost of this version is
£450.00. The card is an 8" x 8" card and densely packed. 196K of 4164 RAM is
fitted, 192K is used for display. The basic resolution is 640 x 288 in two
pages and eight colours. The two pages may be addressed at will, and the use
of two pages allows one page to be displayed whilst manipulation is taking
place on the other. Switching then allows the two display pages to be swopped
instantly making for very fast apparent frame changes. (A Baby Pluto is the
same but only has half as much RAM and a single page.)
The Card is port driven, control codes being sent to three ports
addressed in page CXH. The port addresses may be redefined. Output is provided
in TTL compatible RGB with mixed or separate syncs only, the resolution of the
Pluto precludes the use of an RF output.
Most, but not all the RAM is assigned to the physical display. Areas.
are set aside for the storage of character sets and shapes as desired. These
areas are setup dynamically, and are assigned as pages 0 =- 255. Pages O and 1
are the display pages, setting software switches allows access to any page.
The card uses an 8088 16 bit processor for control
Single and multibyte commands are passed to the on-board 8088 and this
processor causes the function to take effect. The functions provided in the
command ROM as supplied are adequate, but the more complex functions such as
circle drawing and filling and complex fills are only provided with the
extended command ROM available as an option. Little external software is
required to drive the Pluto card.
The Nascom Card.
The Nascom AVC is a 10" x 8" card and is supplied complete with a NAS-DOS
disk of add-ons to the Nascom Basic and a very extensive manual. The card
is the cheapest of the trio at £149.95.
The Nascom AVC has page moded RAM and uses three overlayed RAM planes
each of 16K, which could provide a maximum resolution of 512 x 256. However,
as this RAM is also addressed during line and frame blanking the display is
actually 392 x 256 pixels. The RAM areas being page mode can be addressed at
the same address and as supplied are set to 8000H although these addresses may
be changed to suit at any 16K boundary. As addressing is by page mode, no
space is normally used in the processor RAM plane, but unlike the Pluto and
Climax cards, this method allows direct access to the video RAM. Three ports
are also used for control of AVC via the 6845 video controller allowing non-standard
video formats to be set up (not advised unless you know exactly how
the 6845 works), current cursor positions, ete.
1 volt video outputs for Red, Green and Blue are provided with both
separate and mixed syncs. TTL output levels are also available on the card. An
external connector allows the Nascom PIO to be connected to an area of logic
which can deselect the colour outputs completely or select different colours
to the different outputs, for instance, the red output may be turned off or
may be directed to either the blue or green outputs, and likewise for the
other outputs. This allows very high speed colour switching and use of this
feature allows for limited animation graphics. It’s a pity that horizontal and
vertical syncs are not provided as separate ouputs from the card as we had to
build a primitive RC sync separator to feed frame pulses back into the Nascom