Measurement Computing DBK70 - Manual (Page 70)

6-4 Fundamentals of Obtaining Vehicle Data 928494 DBK70 User’s Manual
As the DBK70 receives network messages, it processes each of the bytes one-at-a-time, comparing each
with its associated 2-byte-set in the Filter definition. The DBK70 processes each byte in the header by first
comparing it, bit-for-bit, with the Pattern Byte. The result of the comparison is then ANDed with the Mask
Byte. A zero in the Mask Byte represents a Don’t Care which results in a 1 when ANDed with
either a 1 or 0.
Filter definitions must be as specific as possible so as not to pass inappropriate messages to the output
channel.
The don’t care bits are used in instances where specific bit values in the header are not significant.
For example, if only the PID byte was significant and the Source, Target, and other header bytes were to be
ignored, the Filter for a 5 byte header would appear as follows.
In this example, any header with a PID byte of 0C(hex) would be accepted and its parameter value would
be processed, regardless of the byte values found in the other bytes.