16x16 or 32x32 pixel sprites by simply changing a number in
the sprite attribute table of the sprite in question.
The 32 planes can be regarded as one ‘above’ another so that
a higher order sprite will eclipse a lower order sprite
giving a 3D effect.
Both sprites and 8x8 pixel blocks on the pattern plane are
called up by naming their shapes in a table, hence any shapes
which are the same are only defined once with a consequential
saving in memory.
The 16K of on-board screen memory is directly interfaced to
and is loaded via an I/O port and an
auto-incrementing address register. This memory is primarily
the screen RAM for the processor but it could be used to
supplement the user’s own memory area.
The sync output from the TMS9929 is fed to a CTC so that
timing may be triggered from field fly-back. This could be
useful in split screen applications, since for many systems a
number of screens can be held in the 16K memory and simply
swapping internal pointers flips from one screenful of
information to another.
Loading the screen memory and control of the TMS9929 is
completely asynchronous with screen access, hence one
screenful of information can be displayed whilst another is
being assembled in the 16K address space without any
disturbance in the displayed video.
A CTC is resident on the board with three of its
outputs/inputs brought to a plug, enabling any desired
timing/counting operations to be used.
An eight channel eight bit A-D converter is also resident on
the board with eight channels available to the user, read as
I/O ports. These are general purpose and would probably be
used for such things as josticks for games or to read sensors
for control applications.
Although the A-D reference voltage is normally the 5 volt
supply, there is a link option to allow the user to fit a
precision 5 volt reference if a specific number of millivolts,
per bit of resolution is required.
Twin sound generators are included on the board to enable
either stereo sound to be formed or else a larger variety of
individual sounds. These generators are again accessed via
the I/O ports. The output from the generators does need to be
amplified by some external means. Not too difficult.
The sound generator clock may be defined either by dividing
down from the 2/4 MHz system clock er by an on-board crystal
oscillator, the frequency of which may be chosen by the