TM 5-6675-316-14
(1) Cursor speed counter. The operator controls cursor movements from the
keyboard. Two keys are provided for this purpose. Depressing one key causes the
cursor to move toward the right of the monitor screen. The other key moves the
cursor to the left. Single keystrokes move the cursor one character block; however,
if the key is held down, the cursor speed counter moves the cursor at a steady rate
until the key is released.
As the cursor speed counter controls the speed of movement, the cursor control
circuit makes these commands available to the data bus. The output of the cursor
control circuit is a level signal generated by either key. Holding the key down for
more than 300 msec causes the cursor speed counter to generate a 30 Hz pulse, and
this is fed into the data bus via the cursor control circuit 1/0 gates.
(2) Data multiplexer. The data multiplexer takes data from the standard
program interface, and keyboard data from the keyboard. This data is then selected
and transferred to the character generator board. The erase circuit operates when
the four bottom lines on the monitor are transferred to the top. Prior to this
taking place, the erase circuit erases the top four lines. While this is taking
place, the ERASE input to the data multiplexer disables both inputs, and outputs all
zeros to the display memory, to clear the memory.
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