Two boards comprise the distribution subsystem: The Aft Distribution Board and the CPU Power Board.

Aft Distribution Board

The Aft Distribution board contains 5 full ports and one hydrophone port. In addition, it supplies +5V to the infrastructure stack and communicates the status of the subsystem to the CPU via TTL-level RS-232 that is routed to the serial board.

The isolation and voltage conversion is accomplished by DC-DC converters. The DC-DC output voltages and currents are measured and fed into an 11-channel, 8-bit ADC for interpretation by the microcontroller. If any values are out of range, the load on the respective DC-DC will be released.

Power then flows to the ports. A switch controlled by the microcontroller can turn the port on and off, and the current flow into the port is measured. The final output powers a green LED before leaving the board, via a connector, to a device.

The current measurement at each port is compared to a threshold value generated by a 4-channel, 8-bit DAC. The DAC output is then compared to each port’s output voltage, and the result is passed to an 8-to-3 priority encoder. In the case of a fault, the encoder generates the binary representation of the faulting port number and an interrupt signal for the microcontroller. The microcontroller can then shut off the port via its switches and turn on a red LED to indicate a fault.

A temperature sensor also feeds into the ADC to provide ambient temperature measurement.

Direct +5V power is provided to the infrastructure stack via the serial board connector, and direct +12V power is provided to 2 fan connectors.

CPU Power Board

The CPU Power Board is an extension of the main distribution board. It contains a large, high-power DC-DC to convert the battery voltage (from the merge board) to the appropriate voltages for the CPU. Output current is fused but not switched; if the board's comperators indicate that the CPU is drawing excessive current, they will simply report this condition to the main distribution board, but will not automatically switch off the CPU.

The CPU Power Board also contains Ethernet Port. This supplies power to the wireless buoy while passing through the data lines from a standard RJ-45 connector leading to the CPU. The board communicates its status, along with a device-side ground reference, back to the Aft Distribution board via 2 TTL-level lines.