Serial transports
Agree on electrical signalling, framing, timing and addressing before decoding serial messages. Check the settings and supported interfaces at both ends.
Sources and scopeSource record 25 August 2026
Technical source record: 25 August 2026. Check the linked documentation for current product requirements.
TIA electrical standards are licensed; exact pinout, voltage, topology, termination, timing, and protocol are product and site specific.
On this page
Overview#
“Serial” describes a transmission style, not a complete protocol. UART framing, TIA 232/422/485 electrical interfaces, connector/pinout, duplex/topology, and the application protocol are independent choices. A DB 9, RJ style connector, terminal block, or USB adapter doesn't identify the signal standard.
Layer record#
| Layer | Record |
|---|---|
| Electrical | standard/variant, signal levels, single ended/differential, isolation, common mode/ground, surge protection |
| Wiring | connector and pinout, cable, shield/drain, topology, pair allocation, termination, bias, length |
| UART/framing | baud, data bits, parity, stop bits, bit order, idle polarity, flow control, break handling |
| Link/application | address, frame boundary, length, escaping, checksum/CRC, direction, acknowledgement, timing |
TIA 232 is typically point to point and single ended. TIA 422 commonly uses differential drivers for point to point/multidrop receiver arrangements. TIA 485 supports differential multipoint buses and is frequently half duplex, but none of those statements supplies a universal connector or application protocol. Obtain the applicable TIA standard and both product manuals before connecting.1
Receiver and state machine#
Use a fixed maximum frame size, incremental parser, explicit idle/inter character timeout, validated length, checksum/CRC before semantic decode, and a bounded outstanding request state. Separate framing error, parity/overrun, checksum failure, application negative response, timeout, late response, and disconnect.
Don't treat a CRC as security; it detects accidental corruption, not deliberate modification. Don't resynchronise on arbitrary “plausible” bytes without a protocol defined boundary. Use monotonic time for frame and response timers.
Multidrop and direction control#
For two wire half duplex buses, only the intended transmitter may drive at a time. Define driver enable timing, turnaround, collision recovery, addressing, broadcast, bias and termination. USB to serial adapters, terminal servers, and IP gateways add buffering, latency, packetisation, reconnect, modem signal, and configuration behaviour that can violate device timing.
Record gateway serial profile, TCP client/server mode, connection sharing, queue limit, idle close, keepalive, packet boundary algorithm, TLS/management support, firmware, and failure semantics. TCP transport doesn't preserve serial frame boundaries automatically.
Safe connection procedure#
Before attachment, obtain a pinout, measure/confirm signal levels with appropriate equipment, isolate grounds, identify whether the port supplies power, and confirm termination/bias ownership. Use galvanic isolation and surge protection appropriate to the environment. Prefer a listen only isolated tap for observation and an isolated bench for active work.
Connecting a mismatched transceiver can damage equipment, disturb a live bus, release a gate, stop telemetry, or create ground current. Confirm electrical compatibility, isolation, termination, bias, idle state, and recovery on an approved bench before any site connection.