Understanding the communications circuit can help in diagnosing and solving communications related problems. Communications related problems include loss of control, telemetry or both.
Overview
The communications circuit in the Pro 4 is a multi-layer bi-directional system.The physical layer includes the hardware, which is made up of wires and electronic components.Operating on top of the physical layer is the communications interface, or standard for the electrical signals, which defines the characteristics for how the data is transmitted and received. On top of the communications interface is the communications protocol which defines what information is transmitted and its format.The application layer defines how the information is encoded, decoded and acted upon.
Physical Layer
The physical layer includes the transmit and receive components in the ROV and the control panel, the wiring from these to the processors and the external connection points, and the tether that connects the ROV to the control panel.
Communications Interface
The primary communications interface from the ROV through the tether to the control is based upon the RS-485 standard. Within the control panel, this is converted to USB standard for communications from the control panel to the computer.This conversion is through an optically isolated interface adapter. The RS-485 standard is set up to allow multi-party communication so that several devices can co-exist on the circuit at the same time.
Communications Protocol
The communications protocol is a proprietary, but open, standard defined by VideoRay. This information consists of control signals to the ROV and telemetry data from the ROV's sensors to the topside.
Application
The application layer consists of firmware in the ROV, and VideoRay Cockpit software on the topside that includes the user interface.
Communications Sequence Summary
- Based on operator input (or not) VideoRay Cockpit packages the information (encodes it within the protocol) and sends a message intended for the ROV.
- The message is transported from the computer via USB cable to the USB hub and communications interface in the control panel.
- The signal is converted to RS-485 and sent to the ROV via the tether.
- The message is received by the ROV's RS-485 interface.
- If the message is addressed to the ROV, it is passed to the ROV's processor.
- The ROV's processor interprets the message. (decodes the protocol packet)
- The ROV's processor reacts to the message. (sets thrust, tilts camera, etc.)
- The ROV's processor collects information from the sensors (depth, heading, temperature, etc.) and packages this information. (encodes it within the protocol)
- The message is transmitted by the ROV's RS-485 interface to the control panel via the tether.
- The message is received by the communications interface in the control panel.
- The signal is converted from RS-485 to USB.
- The USB signal is passed through the Hub in the control panel to the computer.
- VideoRay Cockpit reads the information and acts on it. (updates instrument displays, etc.)
- The process repeats.