The GPIO ports of the CPi-S series have the same layout as the original Raspberry Pi, but there are some differences. Some ports (RS232, 485) are already connected elsewhere and are not available on the GPIO ports. There is an internal buffer chip for ESD protection.

See pp.5 of the Compute Module 4S datasheet for more information.

The 5V pins can supply a maximum current of 1A. The 3.3V pins can supply a maximum current of 700mA. If both 5V and 3.3V rail pins are used simultaneously, their total power should be kept below 5 watts.

The panel PC's RTC is connected to I2C1, so those pins assigned to I2C1 should not be reconfigured.

The underside of the CPi-S panel PCs expose 12~24VDC power input, 1 RS-232 serial port, 1 RS-485 serial port, 3 USB 2.0 ports, an I2C port, 5V power output, and an RJ45 Ethernet port.

Please note that the I2C pins (SDA and SCL) are 3.3V; the 5V pin is supplied to ensure users have enough voltage and current to power their external devices and does not imply a 5V I2C port.

The USB device port dedicated to programming the Compute Module's eMMC.

The right panel of the CPi-S panel PCs exposes a MicroSD card slot and a stereo audio output jack.

For models with an eMMC, the MicroSD card slot is not electrically connected, so it cannot be used.