Furuno IB-681 manual Receiving, Automatic call mode and receiving operation, SW1 State Remarks

3.2 Receiving

Certain HSD terminals cannot receive the RI signal and therefore cannot receive.

3.2.1 Automatic call mode and receiving operation

Receiving processing depends on the setting of DIP switch SW1 as follows:

SW1 State	Remarks
	The HSD terminal uses the DTR signal to reply. To do this the
	HSD terminal keeps the DTR signal OFF when it is not
OFF (direct call)	communicating. When a call arrives, the HSD modem turns on
	the RI signal, the HSD terminal detects the RI signal and then
	turns on the DTR signal. Then, the HSD modem turns off RI and
	then turns on DSR, CTS, DCD to communicate over land line.
	The HSD terminal does not reply to an address call with the
	DTR signal; the DTR signal is used to show if the HSD terminal
ON (address call)	can send control commands to the HSD modem. When a call
	arrives, the method by which the HSD terminal replies depends
	on DTR status as below.

Address call and DTR ON

When a call arrives, the HSD modem turns RI ON and then acknowledges reception by sending INC to the HSD terminal. (See page 10.) Five seconds after sending INC receiv- ing processing is initiated. When processing is completed, RI goes OFF and DSR, CTS, DCD go ON to communicate over land line.

If the HSD terminal sends the DIC command to the HSD modem, the HSD modem does not initiate receiving processing. This happens in the following instances:

•Overlapping calls (receiving processing cancelled)

•Processing initiated within five seconds after INC is received

If this occurs while the call is being relayed, the CIC command is sent and the HSD mo- dem reinitiates processing.

Address call and DTR OFF

When a call arrives, the HSD modem turns RI ON. This tells the HSD terminal to turn on the DTR signal, which causes the HSD modem to send the INC (indication) signal to the HSD terminal to indicate it is receiving. The HSD terminal then sends the CIC command to the HSD modem which initiates receiving processing. When processing is completed, RI goes OFF and DSR, CTS, DCD go ON to communicate over land line.

When DIC is sent by the HSD terminal instead of CIC, the HSD modem sends the indica- tion VAL. In this case processing is not started. Furthermore, when the CRN command or other three-character command is sent the HSD modem sends the indication INV.

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