ABB PSTX soft starter (built-in Modbus RTU)
Register map(s) for this device, each at the trust rung it earned. Addresses are 0-based
as on the wire. Word order and scaling are confirmed at the hardware-verified rung and at no rung below it.
interop-verified
Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.
| point | address (0-based) | type | scale | unit |
|---|
| fbt_return_value | 512 | U16 | 1 | |
| programmable_analog_input_1 | 513 | U16 | 1 | |
| programmable_analog_input_2 | 514 | U16 | 1 | |
| programmable_analog_input_3 | 515 | U16 | 1 | |
| programmable_analog_input_4 | 516 | U16 | 1 | |
| programmable_analog_input_5 | 517 | U16 | 1 | |
| programmable_analog_input_6 | 518 | U16 | 1 | |
| programmable_analog_input_7 | 519 | U16 | 1 | |
| programmable_analog_input_8 | 520 | U16 | 1 | |
| programmable_analog_input_9 | 521 | U16 | 1 | |
| programmable_analog_input_10 | 522 | U16 | 1 | |
| fbt_control_word | 768 | U16 | 1 | |
| fbt_argument_2 | 769 | U16 | 1 | |
| fbt_argument_3 | 770 | U16 | 1 | |
link settings as documented (unverified): RTU; FC 01,04,15,16; Requires setting parameters: FB interface connector to Modbus RTU, Fieldbus control to On, Com3 function to Modbus RTU slave.
⚠ The motor may start unexpectedly if there is a start signal present when doing any of the actions listed below: Switching from one type of control to another (fieldbus control/hardwire control), Reset all Settings — Starkest reads only; we never write a control register.
bench facts as documented (unverified)
| terminals | Com3 |
| connector | FB interface connector |
| wiring notes | Uses RS485 / Modbus RTU |
| doc revision | 1SFC132089M0201 July 2014 |
field reports — community-sourced, unverified (checked 2026-06-11)
- By default, if no Modbus RTU message is received by the PSTX softstarter for more than 100ms, it will trip on fieldbus communication failure protection (P1E00) and stop the motor. In multi-slave networks where polling cycles exceed 100ms, this causes frequent trips unless parameter 19.4 (Fieldbus failure op) is set to 'Off'. [source]
- confirmed: comms framing [RTU] and function codes — confirmed by ABB PSTX Built-in Modbus RTU Manual (1SFC132089M0201)
- confirmed: comms notes regarding parameter settings (FB interface connector, Fieldbus control, Com3 function) — confirmed by ABB PSTX Built-in Modbus RTU Manual (1SFC132089M0201)
- confirmed: control_warning regarding unexpected motor start when switching control types or resetting settings — confirmed by ABB PSTX Built-in Modbus RTU Manual (1SFC132089M0201)
- confirmed: physical connector (FB interface connector), terminals (Com3), and RS485 physical interface — confirmed by ABB PSTX Built-in Modbus RTU Manual (1SFC132089M0201)
- confirmed: register map addresses (fbt_return_value @ 512/0200h, programmable_analog_input_1-10 @ 513-522/0201h-020Ah, fbt_control_word @ 768/0300h, fbt_argument_2 @ 769/0301h, fbt_argument_3 @ 770/0302h) — confirmed by ABB PSTX Built-in Modbus RTU Manual (1SFC132089M0201)
The trust ladder
Each rung states what it proved and what it did not. Gray until proven; green is earned by hardware only.
- generated — A prompt produced it. Unproven — anyone can regenerate this.
- structure-verified — Decode path is structurally sound (addresses, widths, finite values). Does NOT prove word order or scaling.
- interop-verified — Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.
- simulator-verified — Decoded correctly against a protocol emulator seeded with known-true values — catches word-order/scaling errors vs the emulator, not the physical device.
- hardware-verified x1 — Matched a real device with operator-attested readings as ground truth — the only rung that confirms word order + scaling on the wire.