Epson PC AX Technical Manual page 107

REV.A PRINCIPLES OF OPERATION
2.5.2.2 XT mode
TABLE 2-5-3. DATA COMKUNICATION MODE (XT MODE)
XT
DATA
Keyboard initializing signal (low active)
Clock signal
Keyboard Data wait signal (low active)
Data signal from keyboard.
2.5.3 Description of Interface Signals (AT mode)
2.5.3.1 Clock
*
Synchronous clock for transmitting and receiving keyboard data.
*
The clock is generated from the keyboard.
*
The transmission of data cannot take place even if the keyboard is ready
to transmit when there is a low level signal (data wait) in the clock
line. (data will be saved in the keyboard buffer)
The keyboard checks the clock line during transmission of data and will
stop transmission when it detects there is a 10w level signal.
2.5.3.2 Data
*
Keyboard transmission (keyboard scan code, command code), reception code
(command code) data.
*
This is also the transmission request signal from the host.
level signal is detected in the data line, the keyboard is
reception.
2.5.3.3 Keyboard Data Output (AT mode)
Once a 10w
ready for
When the keyboard is ready to transmit data,
it
checks the c10ck and data
lines for data wait or transmission request. If there are high level signals
in both the clock and da ta lines, the keyboard determines that transmission is
possib1e and starts transmitting. It checks the c10ck 1ine during
transmission and stops data transmission as soon as it detects a low level
signal.
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