TIA/EIA-423-B (commonly called RS-423) is an unbalanced, single-ended electrical standard defining driver and receiver characteristics for serial data interchange. It specifies no connector of its own; instead it is referenced by complete interface standards such as TIA/EIA-449 (RS-449) and TIA/EIA-530-A (EIA-530), where it governs Category II control circuits (local loopback, remote loopback, and test mode). The standard permits a single driver to communicate with up to ten receivers over a shared line at data rates up to 100 kbit/s, with a maximum driver output voltage of ±6 V and a receiver sensitivity of ±200 mV — the same sensitivity threshold as the companion balanced standard TIA/EIA-422-B. Driver slew rate is controlled to suppress crosstalk on multidrop lines.
| SPECIFICATIONS | RS423 | RS422 |
|---|---|---|
| Mode of Operation | SINGLE - ENDED | DIFFERENTIAL |
| Total Number of Drivers and Receivers on One Line | 1 DRIVER 10 RECVR | 1 DRIVER 10 RECVR |
| Maximum Cable Length | 4000 FT. | 4000 FT. |
| Maximum Data Rate | 100kb/s | 10Mb/s |
| Maximum Driver Output Voltage | +/-6V | -0.25V to +6V |
| Driver Output Signal Level (Loaded Min.) | Loaded | +/-3.6V |
| Driver Output Signal Level (Unloaded Max) | Unloaded | +/-6V |
| Driver Load Impedance (Ohms) | >450 | 100 |
| Max. Driver Current in High Z State | Power On | N/A |
| Max. Driver Current in High Z State | Power Off | +/-100uA |
| Slew Rate (Max.) | Adjustable | N/A |
| Receiver Input Voltage Range | +/-12V | -10V to +10V |
| Receiver Input Sensitivity | +/-200mV | +/-200mV |
| Receiver Input Resistance (Ohms) | 4k min. | 4k min. |
Notes
- TIA/EIA-423-B defines electrical characteristics only; there is no standardised connector or pinout associated with the standard itself.
- The RS-423 driver output signal level cells in the comparison table above show “Loaded” and “Unloaded” as category labels rather than values. Per TIA/EIA-423-B, the loaded minimum driver output is ±4 V (across a ≥450 Ω load) and the unloaded maximum is ±6 V.
- The “4000 FT.” maximum cable length figure in the table reflects the low-data-rate limit. At RS-423’s maximum rate of 100 kbit/s the practical cable length is considerably shorter — typically 30–90 m — because the controlled slew rate and cable capacitance become constraining factors.
- RS-423 uses an unbalanced (single-ended) driver paired with a differential receiver, making it partially compatible with RS-422 receivers. This contrasts with TIA/EIA-422-B, which uses a fully balanced differential driver and receiver.
- In TIA/EIA-530-A (EIA-530), RS-423 unbalanced signalling is used exclusively for the three Category II circuits: Local Loopback (pin 18), Remote Loopback (pin 21), and Test Mode (pin 25). All other circuits use RS-422 balanced signalling.
- The common-mode voltage range of the RS-423 receiver is ±12 V, matching the receiver input voltage range shown in the table.
- Power supplies of ±5 V are sufficient for RS-423 operation, an advantage over TIA/EIA-232-F which requires ±5 V to ±15 V driver output swing.
References
- AN-216: Summary of Well Known Interface Standards — Texas Instruments (originally National Semiconductor); covers TIA/EIA-423-B alongside TIA/EIA-232-F, TIA/EIA-422-B, TIA/EIA-562, and TIA/EIA-694 in one summary document.
- AN-1031: TIA/EIA-422-B Overview — Texas Instruments; compares RS-423 unbalanced single-ended operation with RS-422 balanced differential signalling.
- Overview of Serial Communication Standards — Sealevel Systems; comparative reference for RS-232, RS-422, RS-423, RS-449, and RS-530 electrical characteristics.