The SDL is outfitted with various ports with different functionality. For the most part these are the same across all models, but the top port differs between a direct connect SDL500 and a telemetry version.

Pin Numbering

The ports on the SDL bulkheads are Underwater Receptacles (UW-R) that accommodate Underwater Plug (UW-P) connections from various sensors and communication devices. The mating plug’s signals are mirrored to those of the receptacle. For example, pin 1 on the receptacle mates with pin 8 on the plug.

Pins on UW Plug

Figure 1: Pins on UW-Plug


Typical SDL500 Port

Figure 2: Pins on UW-Receptacle


Regardless of whether the UW connector is a plug or receptacle the pins are numbered in the same manner. With the pins on the right and the sockets on the left numbering is done clockwise starting with pin 1 at the 1 o’clock position and ending with pin 8 at the 11 o’clock position.



Figure 3: UW Pin Numbering


Shared Signaling

Receptacle Pin P0 P1 T D A


485A 485A 485A 485A AD12


485B 485B 485B 485B AD13


SDI-12 SDI-12 SDI-12 SDI-12 AD14






P0.Rx P1.Rx 1-Wire RAIN AD15




P0.Tx P1.Tx P2.Rx DIO0 AGND

Note that an underwater plug to flying lead cable can be used on sensor connection ports P0 and D (BAT and GND) to wire an SDL500 to external power devices. This is typically done on remote telemetry models, as they do not have access to external power connections via the top communication port without a splitter.


SDL500 Specific Signals

Direct SDL500 loggers are configured to provide host/sensor SDI-12, host RS-485, and host RS-232 signals on the top port.

Receptacle Pin Signal Direction
1 H_RS485A Input/Output
2 H_RS485B Input/Output
3 SDI-12 SDI-12 sensor or master. Firmware configurable.
4 BAT Connect to external battery or supply power to external sensor.
5 H_RS232TX Output
6 Power In Input
7 GND Signal and Power reference
8 H_RS232RX Input

Power can be supplied to the SDL through either pin 5 or pin 3 when no internal alkaline batteries are installed. With the presence of the SDL internal alkaline batteries, external power must be connected to pin 3 to avoid draining the internal batteries.


SDL500C/I/R Specific Signals

SDL500 loggers outfitted for telemetry (cellular, Iridium, or radio) have a top bulkhead port that is designed to allow the connection of an antenna. With this implementation the host RS-232 ports are lost as well as the ability to provide output power.

Receptacle Pin Signal Direction
1 Host RS-485A Input/Output
2 Host RS-485B Input/Output
3 SDI-12 Data SDI-12 sensor or master. Firmware configurable.
4 Key N/A
5 Key N/A
6 Power In Input
7 Ground Signal and Power reference
8 RF Center & Shield Antenna Connection


Flying Lead Cable

A UW to flying lead cable can be used to access the signals on all ports besides the top bulkhead port on a SDL500 with telemetry. Remember when using a flying lead cable, the pin numbers are mirrored.

Receptacle Pin Plug Pin Wire Color
1 8 Green
2 7 Blue
3 6 Brown
4 5 Red
5 4 White
6 3 Yellow
7 2 Black
8 1 Orange

Note: Observe caution when power is supplied to the data logger. All unused flying lead wires must be protected to prevent damage to nearby electronics.



REV: 16D18

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