13. RS-232D Serial Interface Standard (cont'd) - Introduction to Data Communications

Introduction to Data Communications
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13c. Function of Each Signal

Pin	Name	Description	EIA Circuit
1	GND	Chassis ground	AA
2	TXD	Transmit Data (TXD)	BA
3	*RXD*	Receive Data (RXD)	BB
4	*RTS*	Ready to Send	CA
5	*CTS*	Clear to Send	CB
6	*DSR*	Data Set Ready (DCE Ready)	CC
7	*SGND*	Signal ground	AB
8	*DCD*	Carrier Detect (CD or RLSD) (RLSD - Received Line Signal Detector)	CF
9	n/u
10	n/u
11	n/u
12	DCD2	Secondary Carrier Detect (SRLSD)	SCF
13	CTS2	Secondary Clear to Send	SCB
14	TXD2	Secondary Transmit Data	SBA
15	TxSigC	Transmitter Signal Element Timing - DCE	DB
16	RXD2	Secondary Receive Data	SBB
17	RxSig	Receive Signal Element Timing - DCE	DD
18	LL	Local Loopback
19	RTS2	Secondary Ready to Send	SCA
20	*DTR*	Data Terminal Ready (DTE Ready)	CD
21	SQ/RL	Signal Quality/Remote Loopback	CG
22	RI	Ring Indicator	CE
23	DSRS	Data Signal Rate Selector	CH/CI
24	TxSigT	Transmitter Signal Element Timing - DTE	DA
25	TM	Test Mode

The signals in Bold/Italic are required for a basic asynchronous modem connection.

Data Signals

2	TXD	Transmit Data Data generated by DTE	BA
3	*RXD*	Receive Data Data generated by DCE	BB

Control Signals

4	*RTS*	Ready to Send	DTE wishes to transmit
5	*CTS*	Clear to Send	DCE ready to receive
6	*DSR*	Data Set Ready (DCE Ready)	DCE powered on and ready to go
20	*DTR*	Data Terminal Ready (DTE Ready)	DTE powereded on and ready to go
22	RI	Ring Indicator	Phones ringing

Test Modes

18	LL	Local Loopback	Initiate Local Loopback Self-Test
21	SQ/RL	Signal Quality/Remote Loopback	Initiate Remote Loopback Self-Test
25	TM	Test Mode	Initiate Test Mode

Synchronous Control Signals

21	SQ/RL	Signal Quality/Remote Loopback	Error in received data!
23	DSRS	Data Signal Rate Selector	DTE can dynamically select 1 of 2 data rates

Synchronous Timing Signals

15	TxSigC	Transmitter Signal Element Timing - DCE	DCE generated
17	RxSig	Receive Signal Element Timing - DCE	DCE generated
24	TxSigT	Transmitter Signal Element Timing - DTE	DTE generated

Ground/Shield

1	GND	Chassis ground	Shield DTE side only for noise protection. Do NOT connect to signal ground!
7	*SGND*	Signal ground	Signal return path

Introduction to Data Communications
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