Hitachi 902 - RS-232 C Interface Signal Level and Meaning; Interface Signal; Meaning of Interface Signal

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16.9.3 Interface Signal
Table 16-27 lists the meanings of interface signals, and Tables 16-28 and 16-29 list signal
levels and their meanings.
Table 16-27 Meaning of Interface Signal
Abbreviation Signal Name Meaning of Signal
Direction of Signal
(902 side) (Host side)
FG Frame Ground Frame ground
TXD Trans Data Transmission data →
RXD Receive Data Reception data ←
RTS Request To Send Request to send →
CTS Clear To Send Clear to send ←
SG Signal Ground Signal ground
Table 16-28 RS-232C Interface Signal Level and Meaning
Signal Level
Signal Name
Positive (NOTE 1) Negative (NOTE 1)
TXD
RXD
• SPACE
• Start bit
• Data "0" (NOTE 2)
• MARK (no signal)
• Stop bit
• Data "1" (NOTE 2)
RTS
DTS
• ON
• Data "1"
• OFF
• Data "0"
CTS • ON
• Data "1"
• Data communication allowed
• OFF
• Data "0"
• Data communication prohibited
NOTES: 1. Positive..........................Output +12 V, input +3 V to 15 V
Negative .......................Output -12 V, input -3 V to 15 V
2. Data "0" and data "1" correspond to decimal numbers for the CPU to read/write data or
status, respectively.