RP 1201 - Joint TMC/Sae Recommended Practice For Serial Data Communications Between Microcomputer Systems In Heavy-Duty Vehicle Application: Glossary

Access Time - Two bit times multiplied by the message priority (which ranges from 1 to 8) and added to the idle line time.

Baud - The maximum number of analog signal transitions per second that can occur on a channel. In this coding system, this is the reciprocal of the bit time.

Bit Time - Duration or period of one unit of information.

Character Time - The duration of one character. The character must start with a low logic bit, then eight bits of data (least significant bit first) followed by a high logic level stop bit.

Contention - A state of the bus in which two or more transmitters are turned on simultaneously to conflicting logic states.

Differential Signal - A two-wire process in which both lines are switches as opposed to a single-ended signal wherein one line is grounded and the signal line is switched between logic states.

Idle Line - The condition that exists when the bus has remained in a continuous high logic state for at least ten bit times after the end of the last stop bit.

NOTE: The idle line serves as the delimiter between messages on the bus. A receiver that cannot distinguish between a stop bit and any other high logic state may become synchronized with the bus noting the receipt of 12 consecutive high logic bits. In the absence of errors, the first low logic bit (0) following 12 consecutive high logic bits (1) is the start bit of a message identification character (MID) (that is, the first character of a message).

Idle State - The state that produces high logic level on the input of the bus receiver when all transmitters on the network are turned off.

Message Priority - A measure of message criticality assigned on a scale of 1 to 8 by the appropriate applications document. The most critical message has a priority of one.

Node - A receiver or transceiver circuit connected to the bus.

Start Bit - The initial element of a character defined as a low logic level of one bit time duration as viewed at the output of the bus receiver.

Stop Bit - The final element of a character defined as a high logic level of one bit time duration as viewed at the output of the bus receiver.