BR16F84-1.07 ETC, BR16F84-1.07 Datasheet - Page 5

• Manufacturer Part Number: BR16F84-1.07
• Description: OBD II Interface Chip
• Manufacturer: ETC

CHIP COMMANDS AND RESPONSES:
This section details the information needed to send and receive data to the chip from a host computer. It will
enable you to write your own software to utilize the chip with whatever host computer or other control device
you may wish. If you are using the provided program, you need not read this section. Please note that in the
following discussion, all numerical values are in hexadecimal base unless otherwise mentioned.
GENERAL DISCUSSION OF COMMUNICATIONS
This is an overview of communications between the chip and the host computer or controller. There are
exceptions to these rules which are defined in the more detailed sections of this document. All
communications is via a simple 3 wire serial link. No handshaking is used. The chip listens for a message,
completes the task and then returns the results to the host. Then, it immediately waits for the next message.
The typical exchange to or from the chip is a series of bytes. The first byte is called the control byte. The
concept of the control byte is discussed here because it applies to many of the commands and responses
(but not all; exceptions are noted in the specific commands defined below). Normally, the control byte is
simply a number between 0 and 15 decimal (0-F hex) which indicates how many bytes follow this control
byte. For example, if three bytes are to be sent, the control byte would be 3 decimal (or 03 hex), then the
three bytes would follow; 03, byte1, byte2, byte3. This is the method used to ask the chip to retrieve a
particular item of vehicle OBD data, and it is the method used by the chip to return the Vehicles response to
the request message. Note that this only requires using the lower four bits of the control byte. The upper bits
are reserved for certain special commands and responses. These bits are used for the host computer to
make initial connection with the chip, to set the protocol to be used, and for the chip to return data indicating
success or failure. In particular, note that the chip will set the most significant bit of the control byte if the
action was not successful. If the operation was successful, the upper four bits of this control byte will be zero.
These special uses of the control byte are discussed below, and exceptions where the control byte is not
used are also indicated.
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