Panasonic JB-3300 Technical Manual page 209

(a) Keyboard interface circuit
This circuit converts serial data input from the keyboard into
parallel data. It interrupts the CPU so that the CPU can get data
from the keyboard.
Interrupt request block
Data line reset block
LS 125
IRQ | LS74)
KBDATA
DBO~7 KBCLOCK
HARD RESET
KB Vcc
KB GND
FG
Serial/ Parallel!
block
conversion
(LSI75
PCLK
(9.54MHz )
Clock generator
LS!i25
Software reset buffer
LS't25
*1l: I.C.P.: Overcurrent protective parts
Figure 5-64 Keyboard Interface Block Diagram
(1) Serial data creation
When a key is pressed, 2-byte data (*KBDATA) is input to this
circuit in synchronization with the clock pulses (*KBCLOCK).
When the key is released, Key-Off data is input.
The input data enters the serial/parallel conversion block,
where it 1S converted into parallel data using the clock pulses
from the clock generator.
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