Commands From The System; Reset (Hex Ff) - IBM 5170 Technical Reference

(LEDs) on the upper right-hand corner of the keyboard-are
turned on then off, and must be observed to ensure they are
operational.
Execution of the BAT will take from 600 to 900 milliseconds.
(This is in addition to the time required for the POR.)
The BAT can also be started by a Reset command.
After the BAT, and when the interface is enabled (
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clock
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and
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data
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lines are set high), the keyboard sends a completion code
to the interface-either hex AA for satisfactory completion or
hex FC (or any other code) for a failure. If the system issues a
Resend command, the keyboard sends the BAT completion code
again. Otherwise, the keyboard sets the keys to typematic and
make/break.
Commands from the System
The commands described below may be sent to the keyboard at
any time. The keyboard will respond within 20 milliseconds.
Note: The following commands are those sent by the system.
They have a different meaning when issued by the keyboard.
Reset (Hex FF)
The system issues a Reset command to start a program reset and a
keyboard internal self-test. The keyboard acknowledges the
command with an
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acknowledge
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signal (ACK) and ensures the
system accepts the 'ACK
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before executing the command. The
system signals acceptance of the
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ACK
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by raising the clock and
data for a minimum of 500 microseconds. The keyboard is
disabled from the time it receives the Reset command until the
~
'ACK
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is accepted or until another command overrides the
previous one. Following acceptance of the 'ACK
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the keyboard
Keyboard 4-5