Measurement Computing DBK70 - Manual (Page 80)

6-14 Fundamentals of Obtaining Vehicle Data 928494 DBK70 User’s Manual
The first byte of a 2-byte-set defines the bit-by-bit data values that must be matched by a received message
in order to be accepted by the filter and processed by an output channel. The second byte of a 2-byte-set is
a mask byte that defines which bits are to be checked for a match.
As the DBK70 receives network messages, it processes each of the bytes in the header 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, shown below. 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.