FUJITSU C145-C037-01EN - Manual (Page 61)

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5.4 RS-232C Serial Interface
The RS-232C serial interface is a standard interface of this printer.
5.4.1 Hardware requirements
Signal levels:
–3 V or lower for a mark condition (logical 1)
+3 V or higher for a space condition (logical 0)
Input circuit:
An MC1489AL or equivalent is used to convert from the RS-232C level to the TTL level.
Figure 5.9 shows the RS-232C interface input circuit.
Figure 5.9 RS-232C interface input circuit
Output circuit:
An MC1488L or equivalent is used to convert from the TTL level to the RS-232C level.
A 1000-pF capacitor suppresses noise on the output signal line.
Figure 5.10 shows the RS-232C interface output circuit
1000 pF
+5 V
0 V
Figure 5.10 RS-232C interface output circuit