Operation; Commands To The System Unit - Mitsubishi Electric LS Pro Hardware Technical Reference

Peripheral items

Operation

The keyboard communicates with the keyboard interface in the system unit using two
lines: clock and data. These lines are driven by both the keyboard and the system unit.
The keyboard provides the clock for both transmitting and receiving.
Communication is bi-directional. The system unit can send commands to the keyboard
as well as the keyboard sending scan codes to the system unit. The keyboard first checks
the clock line: if it is low, pending scan codes are loaded into the keyboard buffer; if the
clock line is high the keyboard checks the data line.
If the data line is low the keyboard receives commands from the system unit, if the data
line is high the keyboard sends data to the system unit. The data consists of: one start
bit; eight data bits; and one parity bit. Each time the keyboard takes the clock line high
it checks to see if the system unit is pulling the line low. If the line has been pulled low
the code being transmitted is saved and the keyboard enters the receive mode.
Commands to The keyboard sends data and command codes to the system unit. The commands that
the system unit the keyboard can send are described in the following table.
Command
FEh
FCh
FAh
EEh
AAh
00h or FFh
83ABh
Resend (FEh)
The keyboard sends this command to the system unit if it receives an invalid command,
or a command with bad parity.
Self-test failure (FCh)
If the keyboard RAM or ROM self-test fails, this command is sent.
Acknowledge (FAh)
The keyboard sends this command after receiving a valid input from the system unit.
There are two exceptions: in response to an echo command; and usually in response
to a resend command. However, a resend command will result in an acknowledge
response if acknowledge was the last transmission to the keyboard.
Echo (EEh)
This is sent in response to an echo command from the system unit.
Self-test pass (AAh)
This code is sent to the system unit if the keyboard RAM and ROM self-test is passed.
4/20 LS PRO HARDWARE TECHNICAL REFERENCE
Function
resend
self-test failure
acknowledge
echo response
self-test pass
buffer overflow
identification byte