RS-449 (EIA-449) Serial 37 pin

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Image:connector_dsub37m.png 37 pin D-SUB male connector at the DTE (Computer).

Image:connector_dsub37f.png 37 pin D-SUB female connector at the DCE (Modem).

The RS449 interface is a generic connector specification. It’s not an actual interface. The connector pinning was originally designed to support RS422 for balanced signals, and RS423 for the unbalanced signals. And should have been the successor of RS232.

RS449 is a high speed digital interface - unlike RS232 which uses signals with reference to ground, RS449 V.11 receivers look for the difference between two wires. By twisting the two wires and making a “twisted pair” any stray noise picked up on one wire will be picked up on the other, because both wires pick up the same noise the RS449 differential interface just shifts in voltage level with reference to ground, but does not change with respect to each other. The receivers are only looking at the difference in voltage level of each wire to the other not to ground.

The differential signals for RS449 are labeled as either “A and B” or “+ and -”. In the case of RS449 wire A or + does not connect to B or -. Wire A always connects to A and B connects to B or + to + and - to -. If you do cross the wires you just inverted the data or clock in your interface and they don”t work - be sure to check the polarities.

The EIA RS449 standard specifies the functional and mechanical characteristics of the RS449 interconnection between the data terminal equipment (DTE) in the data communications equipment (DCE) complying to EIA electrical interface standards RS 422 and RS 423.

Pin Name V.24 Dir Description Type
1 101 - Shield Ground
2 SI 112 OUT Signal Rate Indicator Control
3 n/a n/a unused
4 SD- 103 OUT Send Data (A) Data
5 ST- 114 IN Send Timing (A) Timing
6 RD- 104 IN Receive Data (A) Data
7 RS- 105 OUT Request To Send (A) Control
8 RT- 115 IN Receive Timing (A) Timing
9 CS- 106 IN Clear To Send (A) Control
10 LL 141 OUT Local Loopback Control
11 DM- 107 IN Data Mode (A) Control
12 TR- 108.2 OUT Terminal Ready (A) Control
13 RR- 109 IN Receiver Ready (A) Control
14 RL 140 OUT Remote Loopback Control
15 IC 125 IN Incoming Call Control
16 SF/SR+ 126 IN/OUT Signal Freq./Sig. Rate Select. Control
17 TT- 113 OUT Terminal Timing (A) Timing
18 TM- 142 IN Test Mode (A) Control
19 SG 102 - Signal Ground Ground
20 RC 102b - Receive Common Ground
21 n/a n/a unused
22 SD+ 103 OUT Send Data (B) Data
23 ST+ 114 IN Send Timing (B) Timing
24 RD+ 104 IN Receive Data (B) Data
25 RS+ 105 OUT Request To Send (B) Control
26 RT+ 115 IN Receive Timing (B) Timing
27 CS+ 106 IN Clear To Send (B) Control
28 IS n/a OUT Terminal In Service Control
29 DM+ 107 IN Data Mode (B) Control
30 TR+ 108.2 OUT Terminal Ready (B) Control
31 RR+ 109 IN Receiver Ready (B) Control
32 SS 116 IN Select Standby Control
33 SQ 110 IN Signal Quality Control
34 NS n/a OUT New Signal Control
35 TT+ 113 OUT Terminal Timing (B) Timing
36 SB 117 IN Standby Indicator Control
37 SC 102a - Send Common Ground
Name Description Function
AA Shield Ground Also known as protective ground. This is the chassis ground connection between DTE and DCE.
AB Signal Ground The reference ground between a DTE and a DCE. Has the value 0 Vdc.
BA Transmitted Data Data send by the DTE.
BB Received Data Data received by the DTE.
CA Request To Send Originated by the DTE to initiate transmission by the DCE.
CB Clear To Send Send by the DCE as a reply on the RTS after a delay in ms, which gives the DCEs enough time to energize their circuits and synchronize on basic modulation patterns.
CC DCE Ready Known as DSR. Originated by the DCE indicating that it is basically operating (power on, and in functional mode).
CD DTE Ready Known as DTR. Originated by the DTE to instruct the DCE to setup a connection. Actually it means that the DTE is up and running and ready to communicate.
CE Ring Indicator A signal from the DCE to the DTE that there is an incomming call (telephone is ringing). Only used on switched circuit connections.
CF Received Line Signal Detector Known as DCD. A signal send from DCE to its DTE to indicate that it has received a basic carrier signal from a (remote) DCE.
CH/CI Data Signal Rate Select
(DTE/DCE Source>
A control signal that can be used to change the transmission speed.
DA Transmit Signal Element Timing
(DTE Source)
Timing signals used by the DTE for transmission, where the clock is originated by the DTE and the DCE is the slave.
DB Transmitter Signal Element Timing
(DCE Source)
Timing signals used by the DTE for transmission.
DD Receiver Signal Element Timing
(DCE Source)
Timing signals used by the DTE when receiving data.
IS terminal In Service Signal that indicates that the DTE is available for operation
NS New Signal A control signal from the DTE to the DCE. It instructs the DCE to rapidly get ready to receive a new analog signal. It helps master-station modems rapidly synchronize on a new modem at a tributary station in multipoint circuits
RC Receive Common A signal return for receiver circuit reference
LL Local Loopback / Quality Detector A control signal from the DTE to the DCE that causes the analog transmision output to be connected to the analog receiver input.
RL Remote Loopback Signal from the DTE to the DCE. The local DCE then signals the remote DCE to loopback the analog signal and thus causing a line loopback.
SB Standby Indicator Signal from the DCE to indicate if it is uses the normal communication or standby channel
SC Send Common A return signal for transmitter circuit reference
SF Select Frequency A signal from the DTE to tell the DCE which of the two analog carrier frequencies should be used.
SS Select Standby A signal from DTE to DCE, to switch between normal communication or standby channel.
TM Test Mode A signal from the DCE to the DTE that it is in test-mode and can”t send any data.
Reserved for Testing

References

Category:Serial Connectors

 

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