MPC555
/
MPC556
CAN 2.0B CONTROLLER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
16-8
matched to a locked message buffer, that message will be transferred into that mes-
sage buffer once it is unlocked, regardless of whether that message’s masked identi-
fier still matches the receive buffer identifier.
shows mask bit values.
shows mask examples for normal and extended messages. Refer to
for more information on Rx mask registers.
16.3.3 Bit Timing
The TouCAN module uses three 8-bit registers to set up the bit timing parameters re-
quired by the CAN protocol. Control registers one and two (CANCTRL1, CANCTRL2)
contain the PROPSEG, PSEG1, PSEG2, and the RJW fields which allow the user to
configure the bit timing parameters. The prescaler divide register (PRESDIV) allows
the user to select the ratio used to derive the S-clock from the IMB clock. The time
Table 16-6 Receive Mask Register Bit Values
Mask Bit
Values
0
The corresponding incoming ID bit is “don’t care”
1
The corresponding ID bit is checked against the incoming ID
bit to see if a match exists
Table 16-7 Mask Examples for Normal/Extended Messages
Message Buffer (MB)
/Mask
Base ID
ID[28:18]
IDE
Extended ID
ID[17:0]
Match
MB2
1 1 1 1 1 1 1 1 0 0 0
0
—
—
MB3
1 1 1 1 1 1 1 1 0 0 0
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
—
MB4
0 0 0 0 0 0 1 1 1 1 1
0
—
—
MB5
0 0 0 0 0 0 1 1 1 0 1
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
—
MB14
1 1 1 1 1 1 1 1 0 0 0
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
—
RX Global Mask
1 1 1 1 1 1 1 1 1 1 0
1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1
—
RX Message In
1 1 1 1 1 1 1 1 0 0 1
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
3
1
NOTES:
1. Match for extended format (MB3).
1 1 1 1 1 1 1 1 0 0 1
0
—
2
2
2. Match for standard format (MB2).
1 1 1 1 1 1 1 1 0 0 1
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0
—
3
3. No match for MB3 because of ID0.
0 1 1 1 1 1 1 1 0 0 0
0
—
—
4
4. No match for MB2 because of ID28.
0 1 1 1 1 1 1 1 0 0 0
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
—
5
5. No match for MB3 because of ID28, match for MB14.
RX 14 Mask
0 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0
—
RX Message In
1 0 1 1 1 1 1 1 0 0 0
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
—
6
6. No match for MB14 because of ID27.
0 1 1 1 1 1 1 1 0 0 0
1
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
14
7
7. Match for MB14.
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Freescale Semiconductor, Inc.
For More Information On This Product,
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