To run a drive from a PLC or PC over Modbus RTU you change a few drive parameters. The names differ by maker, but the order is much the same, and missing one step gives either «no reply» or «replies, but the motor will not run». The examples below are manufacturer manual values collected in this site's device maps (page numbers on each device page).
1. Select the Modbus protocol
- Some drives do not ship with Modbus. On the Mitsubishi FR-E800, Pr.549 defaults to 0 (Mitsubishi inverter protocol); set 1 for Modbus RTU.
- On the OMRON 3G3JX set C070 to 03 and the 485/OPE selector S7 to 485.
- On the LS ELECTRIC S100, CM.02 = 0 is Modbus-RTU (the default).
2. Station number — some defaults never reply
Station 0 is broadcast, so the device does not reply. The FR-E800 Pr.117 defaults to 0 and the Schneider ATV320 Add defaults to OFF, so left as shipped they answer nothing. Set 1 to 247, unique on the RS-485 line. The Yaskawa V1000 H5-01 defaults to 1F (31), so a request to station 1 gets no reply.
3. Baud rate, parity and stop bits
| Drive | Station default | Baud / format default | Run and frequency via comm |
|---|---|---|---|
| LS ELECTRIC S100 | CM.01 = 1 | 9600 bps 8N1 | DRV = 3, Frq = 6 (Int485) |
| Mitsubishi FR-E800 | Pr.117 = 0 (no reply) | 19200 bps 8E1 | — |
| Yaskawa V1000 | H5-01 = 1F (31) | 9600 bps 8N1 | b1-02 = 2, b1-01 = 2 |
| Schneider ATV320 | Add = OFF (no reply) | 19200 bps 8E1 | — |
| OMRON 3G3M1 | y11 = 1 | 9600 bps 8N1 | F02 = 4, F01 = 14 |
| OMRON 3G3JX | C072 = 1 | 4800 bps 8N1 | A002 = 03, A001 = 03 |
Defaults differ, so match the master (PLC or PC) to the drive or the drive to the master. Every device on one line must use the same baud rate and format. «—» means the value is not in the device map; check the manual.
4. Communication changes apply after a reset or power cycle
Many drives do not apply communication parameters right away. The FR-E800 needs an inverter reset; the ATV320, V1000 and 3G3JX need a power cycle. The 3G3JX C07x parameters cannot be changed over Modbus, only from the operator. If the settings look right but nothing replies, check for the power cycle first.
5. Run command and frequency reference source
If the drive replies but the motor does not turn when you write a run command, this is the usual cause. A drive picks the source of the run command (forward, reverse, stop) and of the frequency reference separately: terminals, keypad or communication. Set both to communication, as in the last column of the table, for Modbus run commands and frequencies to take effect. Changing only one gives half a result, such as «the frequency changes but it will not run».
6. What to do when communication stops
If the cable comes out while running over communication, a drive may keep running on the last command. The OMRON 3G3M1 uses y18 (timeout, default 0 = no check) and y12 (trip immediately, decelerate to stop, keep running, etc.); the ATV320 watches for loss with tto (default 10 s). Set this deliberately for the machine's safety.
7. Saving values written over communication
- LS S100: common-area values changed over communication revert at power-off. Write 0 → 1 to 0h03E0 or save with CNF.48.
- Yaskawa V1000: with H5-11 = 0 an Enter command (0900H/0910H) is needed; the default 1 applies at once.
- OMRON 3G3M1: values written with 06/10/17h are not kept in EEPROM. Write 1 to register number 0900h (frame address 08FFh).
- Values that change all the time, such as the frequency reference, are usually not saved; EEPROM has a write limit.
8. Test with a read first
After setting up, read a read-only value such as status or output frequency before writing anything. If the read works, station, baud rate and wiring are right. Then write the frequency reference, and the run command last. For no-reply troubleshooting see the «No reply from a Modbus device» guide; for turning manual addresses into wire addresses see the address notation guide. Whether a drive's addresses are 1-based or 0-based differs by model; each device map notes it in «Addressing» with the manual's frame examples.
Sources
- LS ELECTRIC LSLV-S100 User Manual V4.3 — pp.281-285 CM group and saving, p.282 DRV and Frq
- Mitsubishi FR-E800 Instruction Manual (Communication) — pp.257-258 Pr.549, 117, 118, 120
- YASKAWA V1000 Technical Manual SIEP C710606 18F — pp.434, 439 H5 settings, p.441 Enter, p.442 b1-01/b1-02
- Schneider Electric ATV320 Modbus Serial Link Manual NVE41308 — pp.31-33 Add, tbr, tFO, tto
- OMRON M1 Series Standard Type User's Manual I669-E1-03 — 8-5 to 8-6 communication parameters, 8-21 Enter command
- OMRON 3G3JX User's Manual I558-E1-02 — pp.4-77 to 4-79 C07x, S7, A001/A002
Published 2026-10-30