User Guide

HDV100A3 Command & Response Manual-1306cr 17
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Broadcast Message
The HDV100A3 supports one broadcast message. Once configured by the
host application, this message will be sent repeatedly by the HDV100A3 at a
programmed time interval. This feature is useful to provide a “heartbeat”
function to the J1708 bus with no overhead to the host application’s
software. Sending 0 in the time value stops the broadcast message from
being sent.
To start a broadcast message the time interval, message slot,
priority, number of data bytes, and the data must be sent to the HDV100A3.
Once sent, the HDV100A3 will send the message out on the bus at the
specified interval. Existing bus traffic or any bus messages sent to the
HDV100A3 from the host application take priority over a pending broadcast
message.
Once a broadcast message is started the “Stop Broadcast 07”
message must be sent before any changes to the broadcast message can be
made. Changing from one time value (17) to another (37) without stopping
the broadcast will cause the HDV100A3 to act erratically.
Byte
Number
Byte
Value
Function
1 01 Start of frame
2 04 Control bytes
3 01 ID byte 1 = J1708 message
4 X7 Set broadcast 7 = On X = Time interval (see chart)
5 0X Message slot number (01 only active at this time)
6 PP Priority (see chart below)
7 YY Data bytes
DATA From 4 to 21 bytes
CS Checksum