| Remarks
| This component allows reading and writing of a character
device. It is attached to the keyboard for input, and a
screen window for output.
The output port contains both status bits and the single buffered
input character (if any). The format is:
- Bit 15: If one, indicates the device is ready to print a character
- Bit 14: If on, indicates that a keyboard character is available
- Bits 0-7: The keyboard character
The Ctrl input controls the device. It is written only if bit 0 of
the WCtrl input is non-zero.
The command format is:
- Bit 15: Start a character write.
- Bit 14: Clear the "keyboard character ready" status bit.
- Bits 0-7: The character to write if bit 15 is on.
All other bits are ignored. Both command bits can be given in
a single cycle. Both commands take an undefined number of cycles
to complete. Completion is indicated by changes in the corresponding
status bits.
Characters may be written only when the status output indicates the
component is ready to print a character.
If an output command is issued before the device is ready,
the results are unpredictable, including possibly affecting the previously
output character.
Similarly, if a keyboard event occurs before the
keyboard character ready bit has been cleared, the stored character
is unpredictable. You should respond to each keyboard character with
a clear command (after first reading the new character).
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