A Made IT project



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 succesor of RS232.

Sub-D37M Sub-D37F
Pin Signal Abbr. DTE DCE
2Signal Rate IndicatorSOutIn
4Send Data (A)SD-OutIn
5Send Timing (A)ST-InOut
6Receive Data (A)RD-InOut
7Request To Send (A)RS-OutIn
8Receive Timing (A)RT-InOut
9Clear To Send (A)CS-InOut
10Local LoopbackLLOutIn
11Data Mode (A)DM-InOut
12Terminal Ready (A)TR-OutIn
13Receiver Ready (A)RR-InOut
14Remote LoopbackRLOutIn
15Incoming CallICInOut
16Signal Freq./Sig. Rate Select.SF/SR+In/OutOut/In
17Terminal Timing (A)TT-OutIn
18Test Mode (A)TM-InOut
19Signal GroundSG  
20Receive CommonRC  
22Send Data (B)SD+OutIn
23Send Timing (B)ST+InOut
24Receive Data (B)RD+InOut
25Request To Send (B)RS+OutIn
26Receive Timing (B)RT+InOut
27Clear To Send (B)CS+InOut
28Terminal In ServiceISOutIn
29Data Mode (B)DM+InOut
30Terminal Ready (B)TR+OutIn
31Receiver Ready (B)RR+InOut
32Select StandbySSInOut
33Signal QualitySQInOut
34New SignalNSOutIn
35Terminal Timing (B)TT+OutIn
36Standby IndicatorSBInOut
37Send CommonSC  
Sub-D9M Sub-D9F
2Secondary Receiver ReadySSR  
3Secondary Send DataSSD  
4Secondary Receive DataSRD  
5Signal GroundSG  
6Receive CommonRC  
7Secondary Request To SendSRS  
8Secondary Clear To SendSCS  
9Send CommonSC  

Functional description
Since RS449 is only a newer version of RS232 we will only describe the new signals.

Shield Ground AA Also known as protective ground. This is the chassis ground connection between DTE and DCE.
Signal Ground AB The reference ground between a DTE and a DCE. Has the value 0 Vdc.
Transmitted Data BA Data send by the DTE.
Received Data BB Data received by the DTE.
Request To Send CA Originated by the DTE to initiate transmission by the DCE.
Clear To Send CB 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.
DCE Ready CC Known as DSR. Originated by the DCE indicating that it is basically operating (power on, and in functional mode).
DTE Ready CD 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.
Ring Indicator CE A signal from the DCE to the DTE that there is an incomming call (telephone is ringing). Only used on switched circuit connections.
Received Line Signal Detector CF 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.
Data Signal Rate Select
(DTE/DCE Source>
CH/CI A control signal that can be used to change the transmission speed.
Transmit Signal Element Timing
(DTE Source)
DA Timing signals used by the DTE for transmission, where the clock is originated by the DTE and the DCE is the slave.
Transmitter Signal Element Timing
(DCE Source)
DB Timing signals used by the DTE for transmission.
Receiver Signal Element Timing
(DCE Source)
DD Timing signals used by the DTE when receiving data.
terminal In Service IS Signal that indicates that the DTE is available for operation
New Signal NS 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
Receive Common RC A signal return for receiver circuit reference
Local Loopback / Quality Detector LL A control signal from the DTE to the DCE that causes the analog transmision output to be connected to the analog receiver input.
Remote Loopback RL 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.
Standby Indicator SB Signal from the DCE to indicate if it is uses the normal communication or standby channel
Send Common SC A return signal for transmitter circuit reference
Select Frequency SF A signal from the DTE to tell the DCE which of the two analog carrier frequencies should be used.
Select Standby SS A signal from DTE to DCE, to switch between normal communication or standby channel.
Test Mode TM A signal from the DCE to the DTE that it is in test-mode and can't send any data.
Reserved for Testing    

The secondary signals are used on some DCE's. Those units have the possibility to transmit and/or receive on a secondary channel. Those secondary channels are mostly of a lower speed than the normal ones and are mainly used for administrative functions.