Skip to content

VFD Setup (RS485 / ModBus) for grblHAL

Getting a VFD talking to grblHAL over RS485 is the single most common "why won't my spindle start?" problem people hit. It's not an ncSender issue — ncSender just relays whatever the controller says — but if the handshake between grblHAL and the VFD isn't right, nothing will work.

This page collects the grblHAL settings that matter and the matching VFD parameters for the four VFDs most people run into on hobby / small-shop CNC routers.

Verify against your VFD manual

VFD parameter numbers (PD…, P0…, H00.… etc.) vary by brand, revision, and even year of manufacture — the same "H100 Zhong Hua Jiang" from two different sellers can ship with different code tables. The values below match the most common builds, but always cross-check the manual that came with your VFD before writing settings. If a parameter is locked, look for a "parameter lock" or "advanced menu" code in the manual.

The grblHAL settings you'll touch

ncSender surfaces all of these in the Settings panel — you can search by number. Setting numbers that only appear when a ModBus VFD plugin is compiled into your grblHAL build:

Setting Name Notes
$395 Default spindle at startup Selects which spindle driver is active on boot (PWM, PWM2, Huanyang v1, Huanyang P2A, Durapulse GS20, Yalang YS620, MODVFD, H-100, Nowforever). Requires a hard reset after changing.
$360 ModBus address for the single VFD spindle Default 1. Must match the address configured on the VFD side.
$340 Spindle at-speed tolerance (%) Default 0 (disabled). If >0, grblHAL raises ALARM 14 if the spindle doesn't reach the commanded RPM within ±$340% inside a 4-second window. 10 is a sensible starting value once the VFD is proven.
$461 RPM ↔ Hz relationship Default 60 (60 RPM per Hz — a 2-pole motor). Set to 30 for a 4-pole motor. Used by drivers that compute frequency from RPM (GS20, YL-620 and similar).
$462–$471 MODVFD register overrides Only relevant when $395 = MODVFD. Lets you point the generic ModBus driver at any VFD's registers (run/stop, set-frequency, read-frequency, CW/CCW/stop command words, and RPM ratios). Defaults match the most common register layout.
$476–$479 ModBus address for spindles 0–3 Only used when you have multiple VFD spindles on the bus. For a single-spindle machine, ignore these and use $360.

Baud rate

Baud rate is exposed as a setting on most grblHAL builds — search "modbus" in the Settings panel and you'll see it (numbering varies by driver; commonly $374 or nearby). The default is usually 19200 8N1. Whatever you set here must match the VFD side. 9600 is bulletproof; 19200 and 38400 also work fine on short runs.

Per-VFD picks

Huanyang v1 (HY-series — the yellow-face model)

Pick this if your VFD's front panel says "Huanyang" and uses PD… parameter codes (e.g. PD001).

grblHAL setting Value
$395 Huanyang v1
$360 1
$340 10 (once the spindle is proven)
Baud 9600 (matches PD164=2 below)

Typical VFD parameters — always verify against your PD-code manual:

VFD parameter Value Meaning
PD001 2 Run command source = RS485
PD002 2 Frequency source = RS485
PD163 1 ModBus address = 1 (matches $360)
PD164 2 Baud = 9600 (1=4800, 2=9600, 3=19200)
PD165 3 8N1 RTU

Huanyang P2A (newer, black-face model)

Newer Huanyang. Uses P… codes instead of PD…. Parameter numbers are different — check the manual.

grblHAL setting Value
$395 Huanyang P2A
$360 1
$340 10
Baud Match VFD side (typically 9600 or 19200)

On the VFD side: enable RS485 control (usually in the P00.xx group), set the ModBus address to 1, and set the baud to match. Exact code numbers vary by firmware revision — refer to your manual.

H100 (Zhong Hua Jiang / HuaJiang and rebrands)

Pick this if your VFD shows "H100-1.5C2-1B" or similar and uses H00.… parameter codes. Common with 1.5 kW / 2.2 kW air-cooled spindle kits.

grblHAL setting Value
$395 H-100
$360 1
$340 10
Baud 9600 8N1

On the VFD side: enable RS485 control mode and set the ModBus address to 1. Baud usually defaults to 9600 — check the H00.xx group. If the motor doesn't spin at all, first make sure the VFD works in local (panel) mode with the correct max-frequency and pole-count for your spindle before troubleshooting RS485.

PwnCNC (MODVFD)

PwnCNC ships a VFD pre-configured for RS485 control. In grblHAL you drive it via the generic MODVFD spindle driver, but PwnCNC uses a different register map than grblHAL's MODVFD defaults — you have to write the per-VFD $462–$471 values explicitly. Skipping this step is the most common "spindle spins but ncSender shows wrong RPM / won't stop" complaint.

grblHAL setting Value Notes
$395 MODVFD Numeric value depends on which spindle drivers your grblHAL build has compiled in — pick MODVFD in the ncSender Settings picker; the number underneath will be whatever's correct for that build.
$476 1 ModBus address for spindle 0 (newer multi-spindle builds use $476 instead of $360). Match the address on the VFD.
$374 3 ModBus baud rate — 3 = 19200 on PwnCNC's shipped VFD.
$375 50 ModBus rx timeout (ms).
$340 0.0 PwnCNC ships with at-speed disabled. Raise later once the setup is proven — the safe default is 10 (percent).

PwnCNC register map — set these exactly, not the grblHAL defaults:

Setting Purpose PwnCNC value grblHAL default (wrong for PwnCNC)
$462 Run/stop register 40960 8192
$463 Set-frequency register 40961 8193
$464 Get-frequency register 36864 8451
$465 CW command word 1 18
$466 CCW command word 2 34
$467 Stop command word 6 1
$468 RPM multiplier (write) 25.0 50
$469 RPM divider (write) 60.0 60
$470 RPM multiplier (read) 60.0 60
$471 RPM divider (read) 10.0 100

Diagnosing wrong RPM

If ncSender's spindle RPM display is off by a constant factor (most commonly 10×), you have the wrong $471 — that setting divides the raw ModBus reply into the RPM ncSender shows.

Wiring cheat-sheet

  • Two signal wires — A+ and B-. Some VFDs label them 485+ / 485- or RS+ / RS-; they're the same thing. Keep the pair consistent end to end.
  • Common ground — tie the RS485 GND on the controller side to the VFD's RS485 GND (not the spindle motor ground). Missing this reference causes intermittent packets and phantom ALARM 14s.
  • Twisted-pair, shielded — RS485 is a differential bus; a twisted pair rejects noise. Bond the shield to ground on one end only (usually the controller end).
  • Termination — a 120 Ω resistor across A/B at the far end of the bus. Most VFDs have this built in, enabled via a DIP switch or jumper — check the VFD manual before adding one externally.
  • Cable routing — keep RS485 physically separated from the spindle power cable. Even a foot of parallel run inside a cable chain can induce enough noise to break communication when the spindle ramps.

Verifying it works

  1. Set $395 to the correct driver and hard-reset the controller.
  2. Send M3 S1000 from the ncSender console. The VFD should show the set frequency ramp up and the spindle should start.
  3. If the spindle starts but ncSender's spindle indicator doesn't update (or you see ALARM 14): the write worked but the read isn't — check the ModBus address ($360) and baud match on both sides.
  4. If nothing happens: check wiring (A/B not swapped, ground bonded) before assuming settings are wrong. RS485 has no error message for "no reply" — it just goes quiet.
  5. Once stable, raise $340 from 0 to 10 to enable at-speed monitoring. Program events like G-code tool changes rely on this to wait for the spindle to actually be at RPM before continuing.

Where to go deeper