PiBot V5.88 Ultra — Pin Definition Overview

FluidNC & grblHAL 6+1 Axis CNC Controller · ESP32-S3

The ports of FluidNC can all be freely defined and allocated through the YAML file, so there is no fixed PinMap.

Our current definition is based on the test YAML we use.

When applying it to your machine, you will need to define the pins yourself.

PiBot V5.88 Ultra diagram overview with circled numbers 1-24

The circled numbers ①–㉔ on the diagram correspond to the sections below.

Quick Reference — UART Channels

Channel	Physical Port	Pins (Test YAML)	Typical Use
UART0	Main USB 17	—	Firmware flashing, gcode sender
UART1	RS485 terminal 2	TX: GPIO.12 · RX: GPIO.11	Modbus VFD
UART2	RJ12 port 5	TX: GPIO.0 · RX: GPIO.35	Pendant / IO Expander
UART3	Second USB 24	USB-Host (`usb_host`)	USB pendant / HID device

Key to the Circled Numbers

💡 Tip: If you find the following section challenging, don't worry. You can complete the checklist steps first and then come back — it will make much more sense.

Inputs Outputs Power Drivers Interface

1 Input Terminals Inputs

10 optocoupler-isolated input channels arranged in two rows along the top edge.
Compatible input types: standard ON/OFF input, 5V signal switch, or industrial 12V/24V PNP/NPN switches. For safety, connect a resistor of 2.2kΩ or higher in series with the signal terminal when using a 24V supply.
SW-VCC selection: the optocoupler supply follows the SW-VCC jumper (see ④). Default 5V suits standard inputs; select Vmot-Main for industrial switches.
NPN/PNP trigger mode: configure in YAML by adding or removing the :low parameter.
GPIO.3 as input requires jumper selection first (see ⑩).

Terminal	Test YAML Function	Terminal	Test YAML Function
GPIO.42	X limit −	GPIO.37	A limit −
GPIO.41	X limit +	GPIO.36	B limit −
GPIO.40	Y limit −	GPIO.48	C limit −
GPIO.39	Y limit +	GPIO.47	Probe
GPIO.38	Z limit −	GPIO.3	Toolsetter (jumper-selected, see ⑩)

2 Output Groups Outputs

PWM 5V — GPIO.4 GPIO.5 GPIO.45 GPIO.46: output 5V PWM signals or 5V switching signals for controlling spindles, lasers, servos, etc. Requires connection with any GND on the board to form a complete circuit.
- Test YAML: GPIO.45 = spindle PWM (tool 0), GPIO.46 = laser (tool 1), GPIO.4 / GPIO.5 = user digital outputs (M64 P0/M65 P0, M64 P1/M65 P1).
- MOSFET linkage: GPIO.4 and GPIO.5 are interconnected with the onboard MOSFET channels (see ⑥).
RS485 — TX: GPIO.12, RX: GPIO.11 (UART1): isolated RS485 interface for Modbus devices such as VFDs.
- A/B polarity: if A and B are reversed, simply swap them. Reversed connections will not cause device damage.
- Configuration reference: see the ModbusVFD section of the test YAML.
0-10V — GPIO.6 provides the 0-10V analog output for frequency converters (connect GPIO.6 output and GND, then configure to obtain the corresponding voltage).
- Optocoupler switches: GPIO.7 (Out1/Fwd) and GPIO.8 (Out2/Rev) with OUT-COMMON form switch pairs (both ends of optocouplers), usable as standard digital outputs to signal frequency converters.
- Start/stop function: for frequency converters requiring start/stop control, use these forward/reverse optocoupler outputs as the control signals.

3 Variable Resistor for 10V Adjustment Outputs

Function: adjusts the maximum voltage of the 10V output.
Calibration scenario: when issuing maximum output commands (e.g., M3 S24000), if the output voltage does not reach 10V.
Adjustment method: fine-tune this variable resistor until the output voltage reaches exactly 10V.

4 SW-VCC Voltage Selection Inputs

Function: selects the voltage applied to the input-terminal optocoupler side.
Options: 5V (jumper on left, default) OR Vmot-Main (jumper on right).
Usage: keep 5V for standard switches and 5V sensors; select Vmot-Main for industrial 12V/24V switches. Your industrial switch voltage must match Vmot-Main.
Voltage limit: the SW-VCC input circuit is designed for a maximum of 24V — never exceed 24V on Vmot-Main (see ⑦).

5 Expander / Pendant Port (RJ12) Interface

Function: this port provides UART signals for pendant control or an IO expander module.
Pins: UART2 — TX: GPIO.0, RX: GPIO.35 (test YAML baud: 1,000,000).
Expander benefit: the expander provides additional I/O inputs and outputs for the mainboard.
Compatibility: on V5.88 the pendant/expander port and the OLED (㉒) use independent pins — they can be used at the same time.

6 MOSFET Outputs Outputs

Two channels: io.4-MOS-GND and io.5-MOS-GND (Vmot-Main).
Output capability: can output the same voltage as Vmot-Main or switch it off; used to drive inductive loads such as solenoid valves.
Control principle: controlled via GPIO.4 or GPIO.5 by switching the GND connection to complete the circuit (low-side switching).
Voltage note: Vmot-Main is the positive voltage, while the io.4-MOS-GND and io.5-MOS-GND ports serve as GND.
Flyback protection: onboard flyback diodes are provided for inductive loads.

⚠ Load limit: 500mA maximum (Per channel) — the load current passes through the reverse-polarity protection circuit on the Vmot-Main path. For larger loads, use these outputs to drive an external relay or SSR instead.

⚠ Reverse connection of the load will damage the device! Always verify with a multimeter before use.

7 Main Power Input 12–24V Power

Function: the system voltage input that provides stable power to logic, RS485, amplifiers, and other circuits.
Reverse-polarity protection: built in — a reversed connection will not damage the board. Still, please verify polarity before powering up.
Recommended voltage: 24V input is strongly recommended.

⚠ Never exceed 24V. Although the power regulator itself is rated to 30V, the onboard LM358 amplifier and the SW-VCC input circuit (2.2kΩ current-limit design) are limited to 24V. Exceeding 24V will damage components.

8 On-Board Driver Power 12–24V Power

Function (Vmot-Driver): independent power input that supplies the six onboard stepper driver sockets only.
Capacitor rating: our onboard electrolytic capacitors have a 50V withstand voltage rating.
Driver requirements: some onboard driver modules contain capacitors with lower voltage tolerance, while others require >12V to generate proper signals.
Recommendation: 24V is recommended.

⚠ This input has no reverse-polarity protection — a reversed connection may cause damage. Double-check polarity before powering up.

9 Stepper Driver VDD Logic Voltage Selection Drivers

Function: this jumper selects the VDD logic voltage for stepper motor drivers (onboard or external).
SPI drivers: since SPI signals are 3.3V, select 3.3V when using SPI-type (TMC) stepper drivers.
5V drivers: select 5V for external drivers requiring 5V logic signals.
Default setting: 3.3V (jumper on right). Choose according to your specific driver requirements.

10 GPIO.3 Function Selection Interface

Function: this jumper selects the role of GPIO.3.
Input mode: GPIO.3 is routed to the optocoupler input terminal (used as the toolsetter in the test YAML, see ①).
Output mode: GPIO.3 is routed out as a signal output on the EXTRA IO header (see ⑭).
Exclusive use: only one role at a time — set the jumper to match your YAML definition.

11 Onboard Driver Jumper Configuration Drivers

Function: MS1 / MS2 / RST / SLP configuration switches for the onboard drivers — 1 (Logic High) OR 0 (Logic Low).
MS3: NULL on the switch panel — MS3 must be configured in the YAML via I2SO outputs (see ⑫).
Driver variations: some drivers support MS1/MS2/MS3, while others only support MS1/MS2. Some driver boards label these as MS0/MS1/MS2 — set according to actual pin functions.
Scope: the six onboard driver sockets share one setting — this configures all 6 drivers simultaneously.

⚠ When using onboard SPI-type (TMC) drivers, do NOT install these jumpers — these pins are used by the SPI interface. Only use them with standard (step/dir) onboard drivers.

12 MS3 / CS Mapping Drivers

Function: MS3 pin configuration and corresponding I2SO numbers.
Dual purpose: for SPI-type (TMC) drivers, the MS3 pin acts as the Chip Select (CS) signal.

Axis	MS3 / CS	YAML IO
X	X.MS3 / CSX	I2SO.3
Y	Y.MS3 / CSY	I2SO.6
Z	Z.MS3 / CSZ	I2SO.11
A	A.MS3 / CSA	I2SO.14
B	B.MS3 / CSB	I2SO.19
C	C.MS3 / CSC	I2SO.22

13 EN / STP / DIR — Direct to External Drivers Drivers

White terminals: output EN / STP / DIR signals directly to external stepper drivers. Simple — no jumper configuration needed.
The green terminals below them (⑮) carry the onboard driver outputs to the motors — the two terminal types serve different purposes.

Axis	EN	STP	DIR	Axis	EN	STP	DIR
X	I2SO.0	I2SO.2	I2SO.1	A	I2SO.15	I2SO.13	I2SO.12
Y	I2SO.7	I2SO.5	I2SO.4	B	I2SO.16	I2SO.18	I2SO.17
Z	I2SO.8	I2SO.10	I2SO.9	C	I2SO.23	I2SO.21	I2SO.20

14 EXTRA IO Outputs

Header pins: GPIO.3 / GPIO.10 / GPIO.15 / GND.
Test YAML: GPIO.10 = coolant flood (M8 on / M9 off), GPIO.15 = coolant mist (M7 on / M9 off).
GPIO.3 note: available here only in output mode — see ⑩.

15 Onboard Driver → Motor Terminals Drivers

Green terminals: 2B 2A 1A 1B coil pairs — the onboard driver outputs go to the motors through these terminals.
Direction reversal: swap one coil pair (e.g., 1A/1B) to reverse the motor direction, or invert the direction pin in the YAML.

16 SPI Signal Header Drivers

Pins: MOSI / SCK / MISO / I2SO.3.
Test YAML SPI bus: MOSI: GPIO.1, MISO: GPIO.2, SCK: GPIO.21.
Purpose: SPI bus breakout for external SPI stepper drivers; I2SO.3 serves as the Chip Select (CS) signal.

17 Main USB Interface

Function (UART0): used for firmware flashing, configuration, and gcode sender connection.

18 SPI Input to Onboard TMC Drivers Drivers

Function: routes the SPI bus to the onboard driver sockets (WHEN PLUG ON).
Configuration: install this jumper block when using onboard SPI-type (TMC) drivers; remove it when SPI is not needed by the onboard drivers.

19 USB 5V Test Jumper Power

Function: this jumper cap inputs the USB 5V into the circuit for testing purposes (WHEN PLUG ON).
Important: please remove it when using an external power supply.

20 Antenna Connector Interface

Important note: without an antenna connected, there will be no WiFi signal available.

21 Boot / Reset Buttons Interface

Reset: restarts the controller.
Boot: used for entering download mode during firmware flashing (hold Boot, tap Reset, then release Boot).

22 OLED Interface Interface

Pins: GND / 3.3V / GPIO.13 (SCL) / GPIO.14 (SDA) — I2C address 0x3C, 128×64.
Pinout caution: please note the positions of VCC and GND, as some OLED modules have different pin arrangements.
Compatibility: on V5.88 the OLED can be used at the same time as the pendant/expander port (⑤).

23 TF Card Slot Interface

Pins (test YAML): MISO: GPIO.2, MOSI: GPIO.1, SCK: GPIO.21, CS: GPIO.9.
Compatibility warning: avoid using high-speed or high-capacity TF cards, as some may not be compatible with the ESP32 library.

24 Second USB (USB-Host) Interface

Function (UART3): native USB port configured as USB-Host in the test YAML (usb_host, baud 115200).
First-time setup: set $USBCDC/Enable=Off before using this port for the first time.
Power note: this circuit can power the connected USB device in HID mode, but the controller cannot be powered through this USB port.