Furuno Felcom 30 Operator's Manual page 157

Signal descriptions
102 Signal Ground
Digital ground, return line.
103 Send Data
Data transmitted from DTE (PC) to DCE (FELCOM 30/50/70).
104 Receive data
Data Received from DCE (FELCOM 30/50/70) to DTE (PC).
105 Request To Send
OFF requests DCE (FELCOM 30/50/70) to suspend transmission to
DTE (PC).
ON requests DCE (FELCOM 30/50/70) to resume transmission to DTE
(PC).
106 Clear to send
OFF indicates that DCE (FELCOM 30/50/70) cannot accept data from
DTE (PC).
ON indicates that DCE (FELCOM 30/50/70) is prepared to accept data
from DTE (PC).
107 Data Set Ready
Signal from FELCOM 30/50/70 that when ON indicates that a data call
setup is in progress.
108 Data Terminal Ready
Signal from PC. This signal is used in the Hotline mode and indicate
when going from OFF to ON that the PC wants to make a data call.
The PC clears the call by setting the signal from ON to OFF.
109 Receive Signal Indicator
Signal from FELCOM 30/50/70 that when ON indicates that connection
is established and received data will be delivered on circuit 104,
Received Data.
125 Ring Indicator
Signal from FELCOM 30/50/70. This signal is used in the Auto answer
OFF mode and when ON indicates that an incoming call is in progress.
The signal will go OFF when the call is answered by the PC by turning
circuit 108 Data Terminal Ready ON.
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