RS-449 Interface
The EIA RS-449 standard specifies the functional and mechanical characteristics of
the interconnection between Data Terminal Equipment (DTE) and complying
to EIA electrical interface standards RS-422 and RS-423.

Pin		EIA CKT	Description	From DCE	To DCE
A	B
1 2		SI	Shield Signaling Rate Indicator	*C
4 5	22 23	SD ST	Send Data Send Timing	*T	*D
6 7	24 25	RD RS	Receive Data Request to Send	*D	*C
8 9	26 27	RT CS	Receive Timing Clear to Send	*T	*C
10 11	29	LL DM	Local Loopback Data Mode	*C	*C
12 13	30 31	TR RR	Terminal Ready Receiver Ready	*C	*C
14 15		RL IC	Remote Loopback Incoming Call	*C	*C
16 17	35	SR TT	Signaling Rate Selector Incoming Call		*C *T
18 19		TM SG	Test Mode Signal Ground	*C
20 28		RC IS	Receive Common Terminal in Service		*C
32 33		SS SQ	Select Standby Signal Quality	*C	*C
34 36 37		NS SB SC	New Signal Standby Indicator Send Common	*C	*C
Signal Type: D = Data, C = Control, T = Timing Note: On the DB37 connector that is commonly used for RS449; Pins 3 and 21 are undfined B = Return