Serial Communications

Cable & Communication	Networks	Index - Cables & Communication
	RS 449	Index- Serial
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The RS449 standard describes a 37 way D connector for single ended or differential communication.

The 25 way D connector used by RS232 uses a common return on pin 7 - this is one of its significant design weaknesses. The 25 pin connector does not have physical space for the return paths used in differential signalling unless some pins are redefined - which would wreck compatabiltiy.

Accomodating a similar set of handshake signals and allow use of differential signalling brings the need for a larger connector.

RS449 provides on main data channel and a set of link control handshakes. The number of data channels on a link can be increased by extending the number of connections using 9 way D plugs. Signal types can include RS232, RS422 or RS423.

RS232

Signalling rates beyond 2 million bits per second should be possible with differential RS422.

**RS499 Pins**
Pin	Signal	Abbr.	DTE	DCE
1	Shield
2	Signal Rate Indicator	S	Out	In
3	Unassigned
4	Send Data (A)	SD-	Out	In
5	Send Timing (A)	ST-	In	Out
6	Receive Data (A)	RD-	In	Out
7	Request To Send (A)	RS-	Out	In
8	Receive Timing (A)	RT-	In	Out
9	Clear To Send (A)	CS-	In	Out
10	Local Loopback	LL	Out	In
11	Data Mode (A)	DM-	In	Out
12	Terminal Ready (A)	TR-	Out	In
13	Receiver Ready (A)	RR-	In	Out
14	Remote Loopback	RL	Out	In
15	Incoming Call	IC	In	Out
16	Signal Freq./Sig. Rate Select.	SF/SR+	In/Out	Out/In
17	Terminal Timing (A)	TT-	Out	In
18	Test Mode (A)	TM-	In	Out
19	Signal Ground	SG
20	Receive Common	RC
21	Unassigned
22	Send Data (B)	SD+	Out	In
23	Send Timing (B)	ST+	In	Out
24	Receive Data (B)	RD+	In	Out
25	Request To Send (B)	RS+	Out	In
26	Receive Timing (B)	RT+	In	Out
27	Clear To Send (B)	CS+	In	Out
28	Terminal In Service	IS	Out	In
29	Data Mode (B)	DM+	In	Out
30	Terminal Ready (B)	TR+	Out	In
31	Receiver Ready (B)	RR+	In	Out
32	Select Standby	SS	In	Out
33	Signal Quality	SQ	In	Out
34	New Signal	NS	Out	In
35	Terminal Timing (B)	TT+	Out	In
36	Standby Indicator	SB	In	Out
37	Send Common	SC


Pin	Signal	Abbr.	DTE	DCE
1	Shield
2	Secondary Receiver Ready	SSR
3	Secondary Send Data	SSD
4	Secondary Receive Data	SRD
5	Signal Ground	SG
6	Receive Common	RC
7	Secondary Request To Send	SRS
8	Secondary Clear To Send	SCS
9	Send Common	SC


	General information on serial communications