EIA/TIA RS-530

EIA/TIA RS-530-A (DB25)
RS 530-A defines the pinout when using either balanced RS-422 (and RS-485) or unbalanced RS-423 electrical interfaces using a DB25 connector. By using a DB25 connector RS-530 is now frequently used to replace many older standards which defined hideously huge connectors such V.35. (used a whopping 35 pin connector) and RS-449 (used a pretty serious 37 pin connector).

V.35 on DB25 (RS-530-A)
The original V.35 specification defined use of balanced signals over a huge 35 pin connector. V.35 has been obsolete for years (replaced with V.10 and V.11) though the term is still frequently used. Most modern systems that call themselves V.35 use a DB25 connector which has more modest dimensions. The A (+) and B (-) below refer to each signal pair used in balanced serial interfaces. When used with RS-423 (unbalanced) the B (-) are tied to a common ground. Signals marked U under Bal/Ubal are not balanced since they typically change very infrequently (for example once per session) and therefore do not affect TX/RX performance sensitivity - hence speed. BEWARE: RS-530 (without the A suffix) is an earlier standard and is wired differently. This is the 530-A pinout spec.




Pin No. Name Bal/Ubal Notes/Description
1 Shield Cable Shield, connected at DTE only.
2 BA Transmit Data (A+) (a.k.a TxD)
3 BB Received Data (A+) (a.k.a. RxD)
4 CA/CJ RTS (A+) Request To Send
5 CB CTS (A+) Clear To Send
6 CC U Data Communications Equipment Ready (modem/CSU) (a.k.a DSR)
7 AB Signal Ground
8 CF Data Carrier Detect (A+) (a.k.a DCD, CD or RLSD)
9 DD Receiver Signal Element Timing (B-) RX Clock
10 CF - Data Carrier Detect (B-) (a.k.a DCD, CD or RLSD)
11 DA - Ext. Transmit Clock (B-)
12 DB Tramsmit Signal Element Timing (B-) TX CLOCK
13 CB CTS (B-) Clear to Send
14 BA Transmit Data (TD) (B-) (a.k.a TxD)
15 DB Transmit Signal element Timing (A+) TX CLOCK
16 BB Received Data (B-) (a.k.a RxD)
17 DD Receiver Signal Element Timing (A+) RX CLOCK
18 LL U Local Loopback
19 CA/CJ RTS (B-) Request to Send
20 CD U DTE Ready (a.k.a DTR)
21 RL U Remote Loopback
22 RI Ring Indicator
23 AC Signal Ground
24 DA Ext TX Clock (A+)
25 TM U Test Mode