Communication Interfaces

Popoto Digital Interface

Overview

The Popoto Digital Interface (PDI) is a single connector that provides power, 10/100 Mbps Ethernet, full-duplex RS-232 or RS-422 communication, power control, and a 1PPS time-sync input.

Electrical Connections

All signal directions are relative to the OEM modem. Refer to the digital board connector locations figure for the connector's physical location.

PDI schematic connections.

PDI Electrical Pinout

Pin Number	I/O	Pin Name	Notes
1	P	VDD_3V3	+3.3 V out when unit is powered up
2	O	RS-422 TX+	RS-422 transmit positive
3	O	RS-422 TX-	RS-422 transmit negative
4	I	RS-422 RX+	RS-422 receive positive
5	I	RS-422 RX-	RS-422 receive negative
6	I	Power Switch	Short to GND to power down the unit; leave open for normal operation
7	P	GND	Board ground
8	O	ENET_DP0_P	T568A: green/white T568B: orange/white
9	O	ENET_DP0_N	T568A: green T568B: orange
10	I	ENET_DP1_P	T568A: orange/white T568B: green/white
11	I	ENET_DP1_N	T568A: orange T568B: green
12	O	RS-232 TX	RS-232 transmit
13	I	RS-232 RX	RS-232 receive
14	I	1PPS Input	1PPS or general-purpose digital input, +1.8 V to +5 V logic level

Hardware Components

The PDI uses a Molex Micro-Fit 3.0 connector, P/N 0430251400, or equivalent. The recommended contacts are Molex P/N 0462355001. These gold-plated, low-insertion-force contacts are rated for 250 mating cycles and are suitable for 20–24 AWG wire. They can be crimped with Molex hand tool 0638190000; pre-crimped leads may also be used.

PDI User-Side Molex Connector.

PDI Components and Part Numbers

Part Number	Manufacturer	Description
0430251400	Molex	Micro-Fit 3.0 14-position connector receptacle, 3.0 mm pitch
0462355001	Molex	Micro-Fit 3.0 20–24 AWG gold-plated, lubricated sockets
0638190000	Molex	Micro-Fit 3.0 hand crimp tool
2147611215	Molex	Pre-crimped Micro-Fit 3.0 lead, 450 mm length

Mating Cable Notes

• RS-422 mating cables must use twisted-pair wiring for pins 2/3 and 4/5.
• Ethernet mating cables must use twisted-pair wiring, ideally with 100-ohm differential impedance, for pins 8/9 and 10/11.
• Attach or detach the interface only while power is disconnected from the OEM modem to avoid electrical damage.

Gigabit Ethernet Expansion Interface

Overview

The Gigabit Ethernet Expansion Interface provides the third and fourth differential pairs required to enable Gigabit Ethernet on the OEM modem. It is used together with the two Ethernet pairs on the PDI.

Electrical Connections

All signal directions are relative to the OEM modem. Refer to the digital board connector locations figure for the connector's physical location.

Gigabit Ethernet schematic connections.

Gigabit Ethernet Electrical Pinout

Pin Number	I/O	Pin Name	Notes
4	I/O	ENET_DP2_P	T568A/T568B: blue
3	I/O	ENET_DP2_N	T568A/T568B: blue/white
2	I/O	ENET_DP3_P	T568A/T568B: brown/white
1	I/O	ENET_DP3_N	T568A/T568B: brown

Hardware Components

The Gigabit Ethernet Expansion Interface uses a Molex PicoBlade connector, P/N 0510210400, or equivalent. The recommended contacts are Molex P/N 0500798000, suitable for 26–28 AWG wire. They can be crimped with Molex hand tool 2002181900; pre-crimped leads may also be used.

Gigabit Ethernet Interface User-Side Molex Connector.

Gigabit Ethernet Interface Components and Part Numbers

Part Number	Manufacturer	Description
0510210400	Molex	PicoBlade 4-position connector receptacle, 1.25 mm pitch
0500798000	Molex	PicoBlade 26–28 AWG sockets
2002181900	Molex	PicoBlade hand crimp tool
2149202211	Molex	Pre-crimped PicoBlade lead, 75 mm length

Mating Cable Notes

• The pinout is reversed relative to the PDI board to support pre-made Molex cables that connect A.pin1 to B.pin4, A.pin2 to B.pin3, and so on.
• Use twisted-pair wiring, ideally with 100-ohm differential impedance, for pins 4/3 and 2/1.
• Attach or detach the interface only while power is disconnected from the OEM modem to avoid electrical damage.

TTL UART Interface

Overview

The TTL UART Interface communicates with the modem MPU using +3.3 V logic-level UART. The default UART parameters are 115200 8N1.

Electrical Connections

All signal directions are relative to the OEM modem. Refer to the digital board connector locations figure for the connector's physical location.

TTL UART schematic connections.

TTL UART Interface Electrical Pinout

Pin Number	I/O	Pin Name	Notes
1	P	VDD_3V3	+3.3 V out when unit is powered up
2	I	RS232_RX_EN_N	Connect to pin 1, or to 3.3–5 V, to disable the RS-232 transceiver that shares this UART
3	P	GND	Board ground
4	O	UART2_TXD_3V3	UART transmit, +3.3 V logic level
5	I	UART2_RXD_3V3	UART receive, +3.3 V logic level

Hardware Components

The TTL UART Interface uses a Molex PicoBlade connector, P/N 0510210500, or equivalent. The recommended contacts are Molex P/N 0500798000, suitable for 26–28 AWG wire.

TTL UART Interface User-Side Molex Connector.

TTL UART Interface Components and Part Numbers

Part Number	Manufacturer	Description
0510210500	Molex	PicoBlade 5-position connector receptacle, 1.25 mm pitch
0500798000	Molex	PicoBlade 26–28 AWG sockets
2002181900	Molex	PicoBlade hand crimp tool
2149202211	Molex	Pre-crimped PicoBlade lead, 75 mm length

Mating Cable Notes

Attach or detach the interface only while power is disconnected from the OEM modem to avoid electrical damage.

USB Interface

Overview

The USB port is a standard dual-role USB port configured by the Popoto Modem Linux operating system. It supports both host and peripheral connections. Contact info@popotomodem.com if your application requires the USB port.

Connector revision

OEM modem units manufactured before mid-2026 use a Micro-USB connector. Units revised around mid-2026 use a USB-C connector.