What is Serial Data

Serial data is electronically coded information which is transmitted by one computer and received and displayed by another computer. Using an analog/digital circuit, the transmitting computer digitizes the data from sensors, actuators, and other calculated information. Typically, this means that each sensor or actuator value is converted into a one byte (8 bits) binary word before it is transmitted to the receiving computer.

In order to display the data in familiar units that you are used to working with, the receiving computer interprets each binary word as it is received and displays it as an analog voltage, temperature, speed, time, or other familiar unit of measurement.

Serial data gets its name from the fact that data parameters are transmitted, one after another, in series. The display on the receiving computer updates or refreshes once each data cycle, after all data has been received. Therefore the refresh rate of the data is determined by how many words are on the data stream and how quickly the data is transmitted.

The data transmission rate is referred to as the baud rate. Baud rate refers to the number of data bits that can be transmitted per second. For example, if a data stream has 12 parameters, and each parameter is converted into an 8 bit data word, the total size of the data transmission is 96 bits of data (12 words x 8 bits per word.) If this data can be transmitted once every second, the baud rate is 96 bits/second or 96 baud. In this case, the display screen will refresh data values once every second.

In the case of Toyota engine control systems, there are three different types of serial data which can be received and displayed by your Diagnostic Tester, depending on application. These are OBD, OBD-II, and V-BoB. In all three cases, data is digitized by the transmitting computer (ECM or V-BoB) and displayed by the Diagnostic Tester. The main difference between these three data sources are the specific parameters available on the data stream and the speed at which data can be transmitted and refreshed on the Diagnostic Tester display.

Serial Data Sources

Serial data can be received through one of the Diagnostic Link Connectors (DLC), or on applications which do not support serial data, from the Vehicle Break-out Box.

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