9 pin D-SUB female connector.
TIA/EIA-449 (RS-449, 1977) defines a general-purpose serial interface that uses a primary 37-pin DC-37 connector for main circuits and an optional secondary 9-pin DE-9 connector for auxiliary circuits such as secondary transmit and receive data. The electrical characteristics of the balanced signals on this connector are governed by TIA/EIA-422-B (RS-422), which specifies a differential interface with a minimum 2 V output across a 100 Ω load and a receiver sensitivity of ±200 mV. RS-422 supports data rates up to 10 Mbit/s and cable lengths up to approximately 1,200 m at lower rates, making it far more capable than RS-232 over long distances. This connector is used on the PCA-6773 motherboard and similar hardware that implements the RS-449 secondary interface.
| Pin | Signal | Description |
|---|---|---|
| 1 | Tx- | Transmit Data - |
| 2 | Tx+ | Transmit Data + |
| 3 | Rx+ | Receive Data + |
| 4 | Rx- | Receive Data - |
Signals
- Tx- — Negative leg of the balanced differential transmit data pair (RS-422 Category I circuit).
- Tx+ — Positive leg of the balanced differential transmit data pair (RS-422 Category I circuit).
- Rx+ — Positive leg of the balanced differential receive data pair (RS-422 Category I circuit).
- Rx- — Negative leg of the balanced differential receive data pair (RS-422 Category I circuit).
Notes
- The connector is a 9-position D-sub (DE-9) in female configuration on the DTE side.
- All signals use RS-422 balanced (differential) signalling: each circuit is carried as a twisted pair, providing immunity to common-mode noise. The common-mode voltage range is −7 V to +7 V.
- RS-422 specifies a minimum differential driver output of 2 V across a 100 Ω termination load and a receiver sensitivity of ±200 mV.
- Up to 10 receivers may be connected to a single driver in a simplex multidrop configuration.
- Maximum data rate is 10 Mbit/s; maximum cable length is approximately 1,200 m (4,000 ft), though these figures cannot be achieved simultaneously — higher data rates require shorter cables.
- TIA/EIA-449 was formally superseded by TIA/EIA-530-A in 1992, which provides equivalent functionality on the smaller DB-25 connector already common on RS-232 equipment.