EIA/TIA-694, formally titled “Electrical Characteristics for an Unbalanced Digital Interface for Data Signalling Rates Up to 512 kbit/s”, is a TIA electrical-only standard that extends the useful signalling rate of unbalanced serial interfaces well beyond the 20 kbit/s ceiling of RS-232. It defines an unbalanced, unidirectional, point-to-point interface and is specifically designed to be interoperable with TIA/EIA-232-F devices. The standard is referenced by TIA/EIA-723 and is closely related to EIA/TIA-562, differing primarily in its wider voltage thresholds and higher data-rate capability. Because it is an electrical-only specification, it must be referenced by a complete interface standard that also defines the connector and functional signals.
Notes
- EIA/TIA-694 specifies no connector of its own; the mechanical interface is defined by whichever higher-level standard references it.
- The receiver thresholds of ±2 V are lower than both RS-232 (±3 V) and EIA/TIA-562 (±3 V), allowing reliable detection of the reduced driver output levels produced by lower-supply-voltage circuitry.
- Interoperability with TIA/EIA-232-F devices is explicitly supported: an EIA/TIA-694 driver can drive a standard RS-232 receiver, and vice versa, subject to cable-length and capacitance constraints.
- Driver transition time is controlled to suppress high-frequency energy and reduce crosstalk on shared cables.
Signals
- Driver Open Circuit Output Voltage — must not exceed ±5.5 V to ensure compatibility with RS-232 receivers.
- Driver Loaded Output Voltage (3 kΩ load) — minimum ±3.0 V into a 3 kΩ load, ensuring sufficient signal margin at the receiver.
- Driver Short Circuit Current — limited to ≤100 mA to protect driver circuitry under fault conditions.
- Driver Transition Time Controlled — rise/fall times are controlled to limit spectral bandwidth and crosstalk on the interconnect.
- Receiver Input Resistance — minimum 3 kΩ, consistent with the loaded-driver voltage specification.
- Maximum Receiver Input Voltage — ±12 V; the receiver must tolerate this without damage.
- Receiver Thresholds — ±2 V; signals above +2 V are logic 0 (SPACE) and below −2 V are logic 1 (MARK), matching the polarity convention of RS-232 but with narrower thresholds.
References
- AN-216: Summary of Well Known Interface Standards — Texas Instruments; covers TIA/EIA-694, TIA/EIA-562, TIA/EIA-232-F, TIA/EIA-423-B, and TIA/EIA-422-B in a single summary document.
- Fundamentals of RS-232 Serial Communications — Analog Devices; RS-232 voltage levels, connector types, and related electrical standards including EIA/TIA-562.