Kyocera KM-4230 Service Manual page 152

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(1) Operation unit left PCB

Figure 2-3-9 Operation unit left PCB block diagram

Selection of key switches and the lighting of LEDs are determined by scan signals

(SCAN L1 - L3) and LED signal selection signals (DIGLED L1 - L4). The key switch

operated is identified by the scan signals (SCAN L1 - L3) and the return signals

(DIGKEY L1 - L3).

As an example, to light LED 1, the LED lighting selection signal (DIGLED L1) should be

driven low in synchronization with a low level on the scan signal (SCAN L1). Transistor

TR1 conducts and LED1 is lit. LEDs can be lit dynamically by repeating such

As an example, if KEY1 is pressed, the corresponding key switch is turned on feeding

the low level of the scan signal back to the operation unit main PCB (OMPCB) via the

return signal (DIGKEY L1). The operation unit main PCB (OMPCB) locates the position

where the line outputting the scan signal and the line inputting the return signal cross,

and thereby determines which key switch was operated.

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