MPC555
/
MPC556
CAN 2.0B CONTROLLER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
16-12
a. The control/status word of all message buffers must be written either as
an active or inactive message buffer.
b. All other entries in each message buffer should be initialized as required
3. Initialize mask registers for acceptance mask as needed
4. Initialize TouCAN interrupt handler
a. Initialize the interrupt configuration register (CANICR) with a specific
request level
b. Set the required mask bits in the IMASK register (for all message buffer
interrupts), in CANCTRL0 (for bus off and error interrupts), and in
CANMCR for the WAKE interrupt
5. Negate the HALT bit in the module configuration register
a. At this point, the TouCAN attempts to synchronize with the CAN bus
NOTE
In both the transmit and receive processes, the first action in prepar-
ing a message buffer must be to deactivate the buffer by setting its
code field to the proper value. This step is mandatory to ensure data
coherency.
16.4.3 Transmit Process
The transmit process includes preparation of a message buffer for transmission, as
well as the internal steps performed by the TouCAN to decide which message to trans-
mit. For the user, this involves loading the message and ID to be transmitted into a
message buffer and then activating that buffer as an active transmit buffer. Once this
is done, the TouCAN performs all additional steps necessary to transmit the message
onto the CAN bus.
The user should prepare or change a message buffer for transmission by executing
the following steps.
1. Write the control/status word to hold the transmit buffer inactive (code =
0b1000)
2. Write the ID_HIGH and ID_LOW words
3. Write the data bytes
4. Write the control/status word (active Tx code, Tx length)
NOTE
Steps one and four are mandatory to ensure data coherency.
Once an active transmit code is written to a transmit message buffer, that buffer begins
participating in an internal arbitration process as soon as the receiver senses that the
CAN bus is free, or at the inter-frame space. If there are multiple messages awaiting
transmission, this internal arbitration process selects the message buffer from which
the next frame is transmitted.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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