Channel example - Simple mask

This example extends example Channel example - Single ID to demonstrate a simple use of the filter message ID mask (msgIDMask).

We want to create a filter which accepts two standard ID messages with specific message IDs (using only Channel 1)[1]:

ID 1: $2000_{10} = \text{7D0}_{16} = 11111010000_2$
ID 2: $2001_{10} = \text{7D1}_{16} = 11111010001_2$

Note

Note that the binary representation of the IDs are identical except for the rightmost bit.

To do so, we enable Channel 1 (channelEnb to true) and enable filtering (filteringEnb to true).

The filter msgID can be set to either of the two message IDs, we arbitrarily select $\text{7D0}_{16}$
The filter msgIDMask is set to all ones except for the rightmost bit, $11111111110_2 = \text{7FE}_{16}$ [2]

Note

Setting the rightmost bit of the filter mask to zero effectively makes the filter ignore the value of rightmost bit.

To test if messages with both ID $\text{7D0}_{16}$ and $\text{7D1}_{16}$ pass the filter, we apply the filter mask to both the filter message ID (1 in below) and the message IDs (2 in below)[3]. As the results are equal, both message IDs are accepted by the filter.

Note

In below X is used to indicate either 0 or 1 as the value of the bit does not matter (due to the mask)

$\begin{split}\begin{array}{cc} \begin{array}{cc} \begin{array}{l} \text{Filter ID}\\ \text{Filter mask}\\ \text{Masked filter} \end{array} & \begin{array}{r} 11111010000_2\\ \&\color{green}{1111111111}\color{red}{0_2} \\\hline 11111010000_2 \end{array} \end{array} (1) & \begin{array}{cc} \begin{array}{l} \text{Message ID}\\ \text{Filter mask}\\ \text{Masked ID} \end{array} & \begin{array}{r} \text{1111101000X}_2\\ \&\color{green}{1111111111}\color{red}{0_2} \\\hline 11111010000_2 \end{array} \end{array} (2) \end{array}\end{split}$

The resulting channel configuration becomes:

Compact overview of channel configurations
CHN[4]	channelEnb	extendedID	DSP[5]	filteringEnb	msgID	msgIDMask
1	true	false	1	true	7D0	7FE
2	false	false	1	false	00000000	1FFFFFFF
3	false	false	1	false	00000000	1FFFFFFF
4	false	false	1	false	00000000	1FFFFFFF
5	false	false	1	false	00000000	1FFFFFFF
6	false	false	1	false	00000000	1FFFFFFF
7	false	false	1	false	00000000	1FFFFFFF
8	false	false	1	false	00000000	1FFFFFFF