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The Modem M64 is a two-way half-duplex 64bps acoustic modem with a robust and user configurable data link.

The M64 sets a new market standard with its record-breaking physical size, low power requirement and cost. All this combined with a very useful technical specification, the M64 opens new possibilities for underwater communication in both existing and new areas.

LED Signals

  • No green light: Power is off.

  • Flashing green light (every 3 seconds): Modem is trying to pair with another modem.

  • Fixed green light: Modem has sync with another modem. The LED will blink each time it receives a packet from the other modem (once a second).

Wiring interface

The tables below shows the pinning of the Modem-M64 interface. Depending on which cable type is used, the power wires may have different colors.

Interface Color (Belden) Color (4TP1P)
Positive (10-18V) Orange Red
Negative/Ground Orange/White Black
UART RX Brown Brown
UART TX Brown/White Brown/White


Power must be applied to the power terminals before applying voltage to UART pins

Terminal Interface

The Modem-M64 has a 3.3 volt UART interface.

Settings Value
Baud rate 115200
Data parity stop 8N1
Flow control None


Modem M64 supports channels 1-7.

From (kHz) To (kHz) Channels using this frequency band
31.25 62.25 1
62.25 93.75 2 (16)
93.75 125.00 3 (16)
125.00 156.00 4 (17)
156.00 187.00 5 (17)
187.00 218.00 6 (18)
218.00 250.00 7 (18)

Please note that the Underwater GPS Explorer kit channels 16, 17, 18 overlaps and all channels overlaps with Underwater GPS G2.

Libraries and code examples

Example code and libraries that can be used to communicate with the modem on the terminal interface: