🚀 go-pugleaf

In article <847@m3.mfci.UUCP> colwell@mfci.UUCP (Robert Colwell) writes:
>
>I'm looking at an Intellivision video game for a friend, ca. 1979, which
>seems to only remember how to put out vertical and horizontal sync, but
>nothing else.  I suspect the micro, but the manufacturer glued metal
>heat sinks to the tops of the chips in question and I can't tell what
>they are.  Does anybody out there know?

As I recall, the Intellivision used a Z80 processor driving a Texas
Instruments TMS9918-A display controller.  This is the same graphics
chip that TI used in their 99/4 home computer, but without the
proprietary "GROM" (Graphics ROM).  This is a "sprite"-oriented
graphics chip with several display modes, and it managed its own DRAM
display memory.  The highest resolution it can produce is 256 by 192
with 16 colors from a fixed palette.  It generates a composite video
signal on-chip.  It is theoretically capable of mixing external video
into its display.

It is programmed via a two step, "register-select, data byte" scheme,
with an auto-incrementing address mode for block-loading the display
RAM.  The 9918 runs quite hot so the heatsink is a good idea.  I
believe TI came out with a high-temp version of this part sometime
later.

The 9918 has a number of limitations, including the ability to display
only 4 active sprites on the same scan line.  Any additional active,
lower-priority sprites are blanked.  The result is that in some
complex games, like "Donkey Kong", you will see some of the moving
graphics wink out and wink back on periodically.  There are also
limitations in the number of simultaneous colors you can get within an
8 by 8 pixel block.  All in all, it is a pain to program, but was a
fairly powerful part for the price.






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