Serial Interface Circuit - Citizen CBM-710/720 Service Manual

8.

Serial Interface Circuit

As the serial interface specification, RS-232C and 20 mA current loop can be switched by the slide switch. It can
be switched by the user although fixed by setting at delivery time.
1) RS-232C
By using MAX232C for data receiving (RD), data transmitting and BUSY (DTR), data is transmitted and
received at level of RS-232C. The baud rates of 110 to 9600 bps can be selected by switching the DIP
switch.
2) 20 mA Current Loop
The photo coupler is used for transmitting and receiving. The photo coupler LED is used for receiving data
and the photo transistor for transmitting data.
3) DIP Switch Reading
The baud rate, word length, parity check, parity condition are set by the DTP switch.
4) Positive/Negative Power Supply for RS-232C
±12 V power supply is required for obtaining RS-232C voltage level. In this printer, however, as IC
MAX232C for interface is used, ±12 V is generated at the power circuit built in IC. Thus, no other power
supply is required.
The serial interface circuit diagram is shown in Fig. 8-1.
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CBM-710/720 Service Manual