3.2 Test RS485 Output

Advanced Tests · Optional · Use a USB-to-RS485 adapter and the PiBot VFD simulator

ℹ️

Objective: verify the V4.7B on-board RS485 transceiver and the Modbus VFD commands defined by the supplied I/O-test YAML.

⚠️

Use the simulator first. Do not begin this bench test with a mains-powered VFD or spindle connected. A USB-to-RS485 adapter and computer are sufficient.

PiBot V4.7B
RS485 A RS485 B

A⇄A
B⇄B

USB-to-RS485 Adapter
9600 · 8N1

⚠️

For this simulator test, connect only A and B; do not connect the adapter’s VCC. A/B naming is not consistent across every manufacturer. If the serial port connects but no valid data appears, power down the test wiring, swap A and B once, then retry.

1

Connect the USB-to-RS485 Adapter

Power off before changing the A/B wiring.
Connect V4.7B A to adapter A and V4.7B B to adapter B.
Connect the adapter to the computer and identify its serial/COM port.
Keep the real VFD disconnected during this test.

2

Open the PiBot VFD Simulator

Open PiBot RS485 VFD Simulator.
Select the USB-to-RS485 adapter’s serial port.
Keep the test-YAML serial settings: 9600 baud 8 data bits No parity 1 stop bit.
Click Connect Serial and confirm the simulator reports Connected.

PiBot RS485 VFD simulator showing 9600 8N1 and spindle speed

PiBot VFD simulator reference. Keep 9600 8N1 for the supplied V4.7B test YAML.

3

Send the Commands from FluidNC WebUI

Open the controller WebUI command line and send each command from top to bottom. Wait for the simulator to update before sending the next line.

M6 T3→Select Tool 3: the ModbusVFD configured in the V4.7B test YAML.

M3 S12000→Simulator shows forward/CW running at approximately 12,000 RPM.

M4 S24000→Simulator changes to reverse/CCW and approximately 24,000 RPM.

M5→Simulator returns to stopped.

4

Reference Settings in the Test YAML

Item	V4.7B test setting
UART	UART1 · TX GPIO.15 · RX GPIO.16 · RTS/direction GPIO.14
Serial format	9600 baud · 8N1
VFD definition	Modbus ID 1 · Huanyang model · Tool 3
Speed map	0–24,000 RPM

ℹ️

Shared pins: GPIO.14/GPIO.15 are also used by the 0–10 V Forward/Reverse interface. In the supplied test YAML they are reserved for RS485, so Forward/Reverse contacts are intentionally not assigned at the same time.

✓

Expected Results

The simulator connects to the USB-to-RS485 adapter at 9600 8N1.
M3 S12000 produces the expected forward and speed request.
M4 S24000 produces the expected reverse and speed request.
M5 stops the simulated VFD.
No repeated CRC, timeout or malformed-frame error appears.

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