Key Board Circuit - Samsung SER-6500 Service Manual

11 Operation and Description for each part of the Circuit
11-8-2 Paper End Sensor(Receipt / Journal Paper sensor)
This is the Device to sense the amount remaining of
the Receipt / Journal paper , the photo sensor inside
ERP-300V sense the end of the Receipt / Journal
paper. Therefore the MICOM analyzes this
information and displays paper end message and
the Buzzer is activated.
11-9 Key Board Circuit
The key Circuit consist of the scan signal of 20 lines and the Return signal of 8-line, the scan signals S0-S11
are limited to the 90 Key Board (SER-6540) and the S0-S19 are to 160 Key Board (SER-6500). The U41
(MICOM) sends repeatedly and continuously the scan data S0-S19 through the 74HCT138(U7-U9). The key
Information input in the return signal if the specific key is pressed during the given time. The MICOM reads
the data through U46(74HCT541) and analyzes what key is pressed and transmits this information to the
CPU (U1), then performs the selected function. The U41(MICOM) sends the mode scan signal to the Key-
lock switch and taken the return data through the U46 (74HCT541) And transmits this to the U1(80188) and
performs the selected function.
decoder(74HCT138)
WWW
WWW
pull-up resistor
HCT541
90/160 KEY
U46
Figure 11-14 Key Drive Block Diagram
11-6 Samsung SER-6500 / SER-6500F/ SER-6540 / SER-6540F