EIA/TIA 561 Information from Data Comm for Business, Inc.

Comparison of DCB multiplexer interface and the EIA/TIA 561 interface

DCB uses the RJ45 connector for its SR series products. This decision was made long before there was a standard for this connector (EIA/TIA 561). By chance or by using superior insight, It looks like we did it right.

EIA/TIA 561, Approved March 20, 1990

The standard EIA/TIA 561 specifies a "simple 8 position non-synchronous interface ... employing serial binary data interchange".

Pin#	DCB	EIA/TIA	Comments
1	DSR	RING	DCB applies +12 volts to DSR. It is not under processor control
2	DCD	DCD	Data Carrier Detect
3	BUSY	DTR	Printers and many TTY devices use DTR for flow control
4	SG	SG	Signal Ground
5	RD	RD	Received Data
6	TD	TD	Transmit Data
7	CTS	CTS	Clear to Send
8	RTS	RTS	Is mapped to remote end DCD, as in multi-drop modems and dial up half duplex modems. This is used as the "terminal on/wakeup" to a host computer. On a Unix system, RTS on at the terminal end maps to DCD at the host, which enables a "login" prompt.

DCB designed and implemented the interface before the 561 spec was released. The fact that the interfaces are nearly identical is by chance. (or is it?)

DCB uses pin 3 for busy (DTR), since in 1989/1990, most devices using hardware flow control were printers, directly attached to comm equipment or through a terminal aux port.

Now that we have a proliferation of modems attached to PC's, RTS/CTS has become more common. At this time, DCB has chosen to stay with pin 3 as hardware flow control (if so configured by the user) and RTS is used as a path to the remote DCD signal.

Pos #	SR Terminal Port	Net Mgmt Port	SR Composite Port
DTE/DCE >>	DCE	DTE	DTE
1	DSR (out)	-	RxClk (in)
2	DCD (out)	-	TxClk (in)
3	Busy (in)	DCD (in)	DCD (in)
4	SG	SG	SG
5	RD (out)	TD (out)	TD (out)
6	TD (in)	RD (in)	RD (in)
7	CTS (out)	RTS (out)	RTS (out)
8	RTS (in)	CTS (in)	CTS (in)



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