80-Bus News

Specifications.

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 0 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, etc.

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