DEC VT220 - Page 132

Power-up Test
Upon power-up, the firmware performs a self-test in less than 70
ms. The test results are transmitted to the CPU in four bytes.
The keyboard indicators are lit during t self-test. The
indicators blink once during the self-test routine. The indicators
remain lit if the test is failed, but go off if the test is
passed. The system module can also request a self-test at any
time.
Keycodes
The keycodes represent fix positions in the key switch matrix.
The key associated with a particular matrix position is always
represented by the same keycode.
Special Codes
There are 13 special codes transmitted by the keyboard. Four codes
transmit the results of the power-up self-test. The other nine
codes are status indicators or command acknowledgements.
7.3.2.2 Functions Changed by CPU Instructions -- The CPU can
issue instructions to change some keyboard transmission
characteristics and control the keyboard indicators and beeper.
1 power-up self-test, the firmware
terrnined conditions. These are
itions. The conditions can be changed
to the de ult condition after a
test.
Upon completion of a success
sets certain functions to
referr to as de ult co
but they alwa corne
successful power-up sel
7.3.2.3 Firmware Functions Changed by CPU Instructions -- Certain
firmware functions can be changed by commands (instructions) from
the CPU. These commands are categorized as transmission commands
and peripheral commands. Transmission commands contain a mode set
command and an autorepeat rate set command. Peripheral commands
contain a variety of commands. Refer to section 7.5.5.3 for more
information on peripheral commands.
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