MOTOROLA
Chapter 16. CAN 2.0B Controller Module
16-7
TouCAN Architecture
16.3.1.5 Message Buffer Activation/Deactivation Mechanism
Each message buffer must be activated once it is configured for the desired operation. A
buffer is activated by writing the appropriate code to the control/status word for that buffer.
Once the buffer is activated, it will start the normal transmit and receive processes.
A buffer is deactivated by writing the appropriate deactivation code to the control/status
word for that buffer. A buffer is typically deactivated to reconfigure the buffer (for example
to change the buffer’s function from Rx to Tx or Tx to Rx). The buffer should also be
deactivated before changing a receive buffer’s message identifier or before loading a new
message to be transmitted into a transmit buffer.
For more details on activation and deactivation of message buffers and the effects on
16.3.1.6 Message Buffer Lock/Release/Busy Mechanism
In addition to the activation/deactivation mechanism, the TouCAN also uses a
lock/release/busy mechanism to ensure data coherency during the receive process. The
mechanism includes a lock status for each message buffer and uses the two serial message
buffers to facilitate frame transfers within the TouCAN.
Reading the control/status word of a receive message buffer triggers the lock for that buffer.
While locked, a received message cannot be transferred into that buffer from one of the
serial message buffers.
If a message transfer between the message buffer and a serial message buffer is in progress
when the control/status word is read, the BUSY status is indicated in the code field, and the
lock is not activated.
The user can release the lock on a message buffer in one of two ways. Reading the
control/status word of another message buffer locks that buffer, releasing the previously
locked buffer. A global release can also be performed on any locked message buffer by
reading the free-running timer.
Once a lock is released, any message transfers between a serial message buffer and a
message buffer that were delayed due to that buffer being locked will take place. For more
details on the message buffer locking mechanism, and the effects on message buffer
16.3.2
Receive Mask Registers
The receive mask registers are used as acceptance masks for received frame IDs. The
following masks are defined:
A global mask, used for receive buffers 0-13
Two separate masks for buffers 14 and 15