RS-530 (EIA530) interface pins and signals

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TIA-530 (1987) relies on EIA(RS)-422/423 and uses a differential signaling on a DB25 - RS232 format - EIA-530 Transmit (and the other signals) use a twisted pair of wires (TD+ & TD-) instead of TD and a ground reference as in RS232 or V.24. This interface is used for HIGH SPEED synchronous protocols. Using a differential signaling allows for higher speeds over long cabling. This standard is applicable for use at data signaling rates in the range from 20,000 to a nominal upper limit of 2,000,000 bits per second. Equipment complying with this standard, however, need not operate over this entire data signaling rate range. They may be designed to operate over a narrower range as appropriate for the specific application.  All signals are EIA-422 (balanced) except LL (pin 18), RL (pin 21), and TM (pin 25) which all use EIA-423 (unbalanced). 

TIA-530-A (1992) differs slightly by changing pins 6 and 20 to EIA-423 (unbalanced), adding a Ring Indicator (RI) on pin 22 using EIA-423, and grounding pin 23

Pin	Name	Dir	Description	Circuit	Paired with
1			Shield
2	TxD		Transmitted Data	BA	14
3	RxD		Received Data	BB	16
4	RTS		Request To Send	CA	19
5	CTS		Clear To Send	CB	13
6	DSR *		Data Set Ready	CC	22 (not paired in TIA-530-A)
7	SGND		Signal Ground	Ground
8	DCD		Data Carrier Detect	CF	10
9			Rtrn Receive Sig. Elmnt Timing	DD	17
10			Rtrn DCD	CF	8
11			Rtrn Transmit Sig. Elmnt Timing	DA	24
12			Rtrn Transmit Sig. Elmnt Timing	DB	15
13			Rtrn CTS	CB	5
14			Rtrn TxD	BA	2
15	ST		Transmit Signal Element Timing	DB	12
16			Rtrn RxD	BB	3
17	RT		Receive Signal Element Timing	DD	9
18	LL		Local Loopback	LL	Unbal, not paired
19			Rtrn RTS	CA	4
20	DTR *		Data Terminal Ready	CD	23 (not paired in TIA-530-A)
21	RL		Remote Loopback	RL	Unbal, not paired
22	**		Rtrn DSR	CC	6 (not paired in TIA-530-A)
23	***		Rtrn DTR	CD	20 (not paired in TIA-530-A)
24	TT		Transmit Signal Element timing	DA	11
25	TM		Test Mode	TM	Unbal, not paired