Physical Layout & I/O

Hardware Reference

ALPON X4 physical layout & I/O

Pinouts, ports, indicators, and electrical characteristics for every externally accessible interface on the ALPON X4 industrial edge computer. Use this reference to wire the device, drive its GPIO from software, and plan field installations. Built on Raspberry Pi.

Raspberry Pi CM4 1× Gigabit + 1× 100 Mbps Ethernet 2× USB 2.0 HDMI 2.0 / 4Kp30 RJ45 GPIO 9–30 V DC PoE+ (variant)

ALPON X4 · Hardware Reference · Physical Layout & I/O · Updated 2026-09-17

What I/O does the ALPON X4 expose?

The ALPON X4 exposes 3 power inputs (USB-C PD, 9–30 V DC terminal, optional PoE+), 1× Gigabit Ethernet and 1× 100 Mbps Ethernet, 2× USB 2.0 (1 A shared), HDMI 2.0 for display up to 4Kp30, an RJ45 GPIO Add-on port (I²C / UART / SPI at 3.3 V logic), 4 LED indicators, 2 user buttons, and 2 DIP switches for watchdog and image-flash mode.

Device layout

The ALPON X4 is housed in a fanless aluminum enclosure. All I/O is split between the front face (power, USB, display, indicators) and the rear face (Ethernet, GPIO, antennas, switches). Click any image to enlarge.

Front face

1PB1 · user push button

24× LEDs · Power, Connection, Cellular, RGB

3USB Type-C PD · power input

4Screw Terminal · 9–30 V DC input

5HDMI 2.0 · up to 4Kp30 display

62× USB 2.0 · 1 A shared budget

Rear face

7SW1, SW2 · watchdog & boot/burn DIP switches

8PB2 · user push button

9ETH · 100 Mbps Ethernet port

10ETH/G · 1 Gbps Ethernet (PoE+ on PoE variants)

11GPIO Add-on Port · RJ45, not Ethernet

Enclosure

12Antennas · 2× LTE and 1× GNSS (SMA), 1× Wi-Fi/Bluetooth (RP-SMA)

13Mounting Holes · 2× 4 mm for DIN rail or wall mount

14Heatsink · finned aluminum top face, passive cooling

Mechanical specifications

See Specifications — Mechanical & environmental for enclosure dimensions, weight, and environmental ratings. For the documented mounting holes, bracket kits, and installation steps, use Power & Mounting.

Keep the finned cooling surface unobstructed. For custom brackets or cabinet spacing, ask Sixfab support for verified mechanical guidance before fabrication.

Power input

Choose one power input: USB-C PD, the DC terminal, or optional PoE+ on ETH/G. This section identifies connectors and terminal polarity; see Power & Mounting for adapter requirements, consumption, and the PoE power budget.

Connect only one power input at a time, as required by the Safety & Compliance guidance. Disconnect the active source before changing inputs; do not use simultaneous inputs for failover.

ALPON X4 three power input options: USB-C PD, screw terminal, and PoE+ — Three available power input options on the ALPON X4.

USB Type-C PD

Sink-only USB-PD port. Does not provide USB data or output power during normal operation. USB data is available only when SW2 is set to Burn (image flashing) mode.

Use the documented 15 V / 1.8 A (27 W) PD profile. See USB-C power requirements before selecting an adapter.

Screw terminal (9–30 V DC)

The 3-pin DC terminal accepts 9–30 V. Full peripheral functionality requires 12–30 V at the terminal; below 12 V, peripheral availability is restricted. Check polarity before connecting power.

Screw terminal — pinout

Pinout (3-pin block) Pin 1 Chassis Ground · Pin 2 Negative (−) · Pin 3 Positive (+)

ALPON X4 3-pin screw terminal block pinout: Pin 1 chassis ground, Pin 2 negative, Pin 3 positive — Terminal block polarity, left to right: Chassis, −, +.

Power over Ethernet (PoE+)

On PoE-variant SKUs, ETH/G carries both Gigabit Ethernet data and PoE+ power. The 100 Mbps ETH port is data-only. PoE+ delivers up to 25 W, below the 27 W simultaneous system peak: reduce peripheral load or use DC / USB-C PD instead. See PoE+ requirements and budgeting.

Restricted Mode

Below 12 V, the documented restricted state disables USB, the GPIO Add-on 5 V rail, HDMI, and the RGB LED. Use 12–30 V DC or the documented 15 V USB-C PD profile for full peripheral functionality. See Restricted Mode for low-voltage guidance; do not rely on a low-voltage USB source for boot or connectivity.

Ethernet ports

Two RJ45 Ethernet ports provide different link speeds. Use them for WAN + LAN routing or separate network segments; configure routing and isolation in software.

ETH/G 1 Gbps PoE+

Gigabit Ethernet data, plus PoE+ power input on PoE-variant SKUs.

1 Gbps · optional PoE+

ETH 100 Mbps

100 Mbps Fast Ethernet data port, no PoE.

100 Mbps · data only

PoE+ adds power to ETH/G; it does not replace Ethernet data. Confirm that your SKU includes PoE before selecting a power source. Controller-to-port routing is awaiting hardware confirmation; use the documented link speeds rather than assuming a native or USB-bridge path.

USB 2.0 ports

Two USB 2.0 high-speed ports. Devices connected here are recognized as directly attached to the Raspberry Pi CM4 USB controller. Both ports share a combined 1 A power budget.

USB 2.0 — specifications

Standard USB 2.0 High-Speed (480 Mbps)

Routing Direct to Raspberry Pi CM4 USB controller

Shared power budget 1000 mA total at 5 V across both ports

Overcurrent behavior Power cut to both ports if 1 A is exceeded

Power recovery Full device shutdown and power-on required

You can connect a single device drawing up to 1 A, or two devices with a combined draw of no more than 1 A. If this limit is exceeded, power to both ports cuts off and a full device reboot is required to restore.

Display (HDMI 2.0)

Single HDMI 2.0 port driven directly by the CM4. Connects to a standard monitor with an HDMI cable. Supports up to 4K @ 30 Hz.

ALPON X4 HDMI 2.0 display port close-up, supports up to 4Kp30 — HDMI 2.0 display port, up to 4Kp30.

HDMI 2.0 — specifications

Standard HDMI 2.0

Maximum resolution 4K @ 30 Hz (4Kp30)

Audio HDMI audio pass-through

Driver CM4 HDMI 0 (direct)

Display detection runs at boot. For first-time setup or headless-to-monitor transitions, plug in HDMI before powering the device.

GPIO Add-on port (RJ45)

The GPIO Add-on port exposes six configurable CM4 digital GPIO pins over an RJ45 connector, with I²C, UART, and SPI options for compatible ALPON Edge Add-on modules. Signals use 3.3 V logic. Analog input support is not verified; do not connect analog signals on the assumption that this port provides an ADC.

Although the connector is RJ45, this port is not Ethernet and not PoE-capable. Connecting it to a switch, router, or PoE injector will cause permanent hardware damage. Use only with compatible ALPON Add-on modules.

Pin assignment

RJ45 pin map — CM4 GPIO

Pin 1 GND · Ground

Pin 2 GPIO 12

Pin 3 GPIO 14

Pin 4 GPIO 13

Pin 5 GPIO 15

Pin 6 GPIO 23

Pin 7 GPIO 22

Pin 8 5V OUT · 5 V output, max 1 A. Gated by GPIO 21 power switch

GPIO numbers above identify the documented connector wiring, not an enabled bus configuration. For SoC alternate functions, consult section 2.5.1, Alternative function assignments, in the official Raspberry Pi CM4 datasheet. Confirm the X4 OS pinmux and compatible add-on configuration before enabling a bus; the SoC table alone does not establish X4 carrier support.

Electrical characteristics

Electrical & logic

Signal voltage 3.3 V logic (level converter on board)

5 V tolerance Pins are not 5 V tolerant

Power output 5 V at 1 A maximum (5 W)

Power switch enable GPIO 21 · must be HIGH before I/O

Fault detection GPIO 20 · HIGH normally, LOW on fault

The six GPIO signal pins use 3.3 V logic and are not 5 V tolerant. Driving them above 3.3 V can damage the CM4. Pin 8 is a separate 5 V power output, not a GPIO signal.

Enabling the port from software

The 5 V supply and signal I/O are gated by an on-board power switch. Drive GPIO 21 HIGH to activate the port, then read GPIO 20 to confirm no fault is asserted.

Control signals

ADDON_PWS_EN GPIO 21 · Drive HIGH to activate the port. I/O is inactive while LOW.

ADDON_PWS_FAULT GPIO 20 · Reads HIGH normally. Goes LOW on overcurrent or short-circuit events. Returns HIGH once the fault clears.

# 1. Enable the GPIO Add-on port power rail
pinctrl set 21 op dh      # drive GPIO 21 HIGH
pinctrl get 20            # read fault line, expect 1 (HIGH)

RJ45-to-terminal block adapter

When optional RJ45-to-terminal block adapters are attached, the GPIO port pins are mapped to screw-terminal positions for easy field wiring.

LED indicators

Four LEDs on the front face report system state. All LEDs are driven through the TCA6408A I²C I/O expander at address 0x20 on the I²C1 bus (SDA: GPIO 2, SCL: GPIO 3).

Programmable RGB

User

Expander P2 (R) · P3 (G) · P4 (B)

Logic Active LOW

Freely programmable. Set color by writing the corresponding R/G/B expander pins to LOW.

Cellular Status

System

Driver ALPON X4 OS

Colors Red / Yellow / Blue

Red: poor signal · Yellow: moderate · Blue: good connection.

Connection Status

System

Driver ALPON Cloud agent

Color Green

Green when connected to ALPON Cloud at connect.sixfab.com; off when disconnected.

Power

Hardware

Source System power rail

Behavior Active HIGH

White indicates system power; it does not confirm boot completion or cloud connectivity.

The Programmable RGB LED is controlled through the TCA6408A I²C expander, not direct CM4 GPIO outputs. Expander pins P2 (Red), P3 (Green), and P4 (Blue) are active LOW. Preserve unrelated expander bits when changing color. A reference Python script is available as a GitHub Gist.

Push buttons

Two user-programmable buttons: PB1 on the front face and PB2 on the rear. Both lines are pulled HIGH by default and read LOW while pressed. Both can be assigned to different functions in software.

Button mapping

PB1 (front) GPIO 5 · Pulled HIGH · LOW when pressed · user-defined action

PB2 (rear) GPIO 6 · Pulled HIGH · LOW when pressed · user-defined action

Watchdog & Boot/Burn switches

Two DIP switches sit under a silicone cap on the rear face. Both ship OFF by default and should remain OFF during normal operation. Use a pointed tool to lift the cap from its notch.

SW1 · Watchdog

OFF (default) Watchdog active

ON Watchdog inactive

SW2 · Boot / Burn

OFF (default) Boot · normal operating mode

ON Burn · CM4 image flash mode

SW1 · Hardware watchdog

The hardware watchdog monitors its heartbeat independently of the OS. With SW1 OFF, a missing heartbeat causes a reset. Assign exactly one heartbeat owner: the system watchdog service or an application, never both. A second pulse source can mask a failed application. The watchdog is disabled with SW1 ON; configure the intended owner before enabling it.

SW2 · Boot / Burn mode

SW2 selects between normal operation (Boot) and CM4 image flashing over USB-C (Burn). In Burn mode, the USB-C port exposes the CM4 flashing interface to a host PC.

Power the device off before changing SW2. Restore SW2 to OFF (Boot) after support-guided flashing. SW1 OFF enables the watchdog, so verify its single heartbeat owner before restoring that setting.

If an image is damaged or needs reflashing, contact Sixfab support before attempting the flash. Trying to reflash the image without guidance may cause more issues.

Antenna connectors

Four antenna connectors carry the wireless interfaces: SMA for LTE and GNSS, RP-SMA for Wi-Fi/Bluetooth. Enclosure labels identify each port.

ALPON X4 antennas: G (GNSS), W (Wi-Fi), L x 2 (LTE Main + Diversity) — Antenna labels: G = GNSS · W = Wi-Fi · L × 2 = LTE.

Antenna connector map

LTE Main Label L · SMA Female · Primary cellular RF path

LTE Diversity Label L · SMA Female · Rx diversity for improved link budget

GNSS / GPS Label G · SMA Female · Active antenna · must face the sky

Wi-Fi / Bluetooth Label W · RP-SMA · 2.4 GHz + 5 GHz

Use the supplied Wi-Fi antenna on the RP-SMA port marked W, and the matching SMA antennas on GNSS and LTE ports. SMA and RP-SMA are not interchangeable: check both threads and center contacts, and never force a connection.

Cellular & wireless specifications

LTE band list, Wi-Fi/Bluetooth, and GNSS specs.

Cellular & wireless specifications

Internal bus topology

How each external interface maps back to the CM4. Useful for diagnosing throughput limits and shared-rail behavior.

Interface → CM4 mapping

USB Port 1 + 2 Native USB 2.0 · Direct to CM4 USB controller · 1 A shared budget

ETH (100 Mbps) 100 Mbps data only · controller routing pending hardware confirmation

ETH/G (1 Gbps) 1 Gbps data · PoE+ power input on PoE variants · controller routing pending hardware confirmation

HDMI Display CM4 HDMI 0 · 4Kp30 maximum

LEDs I²C1 → TCA6408A @ 0x20 · Expander-driven

GPIO Add-on Port CM4 GPIO 12–15, 22, 23 · Gated by GPIO 21 power switch

Buttons CM4 GPIO 5 (PB1), GPIO 6 (PB2) · Pulled HIGH, LOW when pressed