Key Circuit - Panasonic KX-DT543-B Service Manual

4.2.8.

Key Circuit

The key detection is under the matrix control by IC150.
The HOOK key is independent from Key Scan Matrix and taken into the port singularly.
KEY Input control timing chart
KEYIN pins have a internal pull-down resistor.
If KEY is pushed, high level is latched by connecting STB(output high) and KEYIN. If not, low level is latched.
The value is fixed by reading twice.
"7"
(SW44)
LED_STB0
(IC150 pin24)
LED_STB1
(IC150 pin25)
LED_STB2
(IC150 pin26)
LED_STB3
(IC150 pin27)
LED_STB4
(IC150 pin28)
LED_STB5
(IC150 pin29)
LED_STB6
(IC150 pin30)
LED_STB7
(IC150 pin31)
KEYIN1
(IC150 pin11)
KEY_CLK
(IC150 Internal)
once
"7"(SW44) button is pressed.
twice
"7"(SW44) is fixed.
13
KX-DT543/KX-DT543-B/KX-DT546/KX-DT546-B
When "LED_STB1" is high status
and the "7" button pressed,
the key-in information is read.