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5-8
5.3.1 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:
A µPD4712 is used to convert signals from the RS-232C level to the TTL level.
Figure 5.6 Serial interface input circuit
Output circuit:
A µPD4712 is used to convert signals from the TTL level to the RS-232C level. A 1000 pF capacitor
suppresses noise on the output signal line.
Figure 5.7 Serial interface output circuit
1000 pF
+12 V
–12 V