Controls — GS21 Modbus
| Field | Detail |
|---|---|
| Primary artifact(s) | controls/water/modbus/gs21-registers.md, controls/water/modbus/gs21-master-config.st |
| Spec | RO-SPEC-001 §5.3 ; WIRE-001 §11.1 |
Summary
Modbus RTU reference for three AutomationDirect GS21 drives on the P2-550 RS‑485 port:
| Drive | Slave ID | Pump |
|---|---|---|
| VFD-101 | 1 | P-101 RO feed |
| VFD-102 | 2 | P-102 recirc/transfer |
| VFD-103 | 3 | P-103 distribution |
38400 baud, 8N1, RTU — matches WIRE-001 §11.1 and drive settings P09.01 = 38.4, P09.04 = 12.
Register map (GS20/GS21 manual Rev E, Ch 5 + Appendix D):
| Function | Hex | Dec (40001+) | Tag(s) | Scaling |
|---|---|---|---|---|
| Frequency command | 2001h | 48194 | MB_WRITE_FREQ_X100_V10x | ×0.01 Hz |
| Output frequency feedback | 2103h | 48452 | MB_READ_OUTFREQ_V10x | ×0.01 Hz |
| Present fault (Status Monitor 1) | 2100h | 48449 | MB_FAULT_WORD_V10x | low byte = fault code |
| Fault reset pulse | 2002h | 48195 | (commissioning / alarms) | bit 1 = Reset command |
Run/stop on JCWS is primarily dry contact (DO_VFD10x_RUN_AUX → MI1); Modbus carries speed setpoint and fault diagnostics. The .st file is an illustrative master-config comment block — recreate identical addresses in Productivity Suite Modbus RTU Master UI.
Previous draft placeholders (
4193,4240) were incorrect offsets; always use the manual formula 40001 + hex and verify ±1 in the IDE.
Test
- Addressing sanity: read
P01.18at 40275 after a keypad tweak (Appendix D procedure). - Speed loop: write 48194 = 1500 with MI1 run closed → read 48452 ≈ 15.00 Hz on GSoft2 + PLC trace.
- Fault path: force a fault, confirm 48449 low byte ≠ 0, pulse 48195 bit 1, confirm clear.
- Three-slave bus: bring up one drive at a time per bench commissioning §5.
Changelog
- 2026-05-24 — Replaced placeholder register numbers with GS20/GS21 manual Rev E map (
48194freq cmd,48452outfreq,48449fault status,48195reset). Documented slave IDs 1–3, 38400 8N1 RTU, driveP09.xx/P00.2xminimums, and Productivity master row template ings21-master-config.st.
Open items
- Confirm Productivity Suite uses 48194 vs 48193 addressing on commissioning PC (±1 toggle)
- Export GSoft2 Modbus map + Productivity master readback to
controls/water/exports/ - Update
tags.csvaddress_refcolumns fromH4193_VERIFYplaceholders after IDE config save
Reviewer sign-off
- Modbus map verified on hardware (all three slaves) — _______________