CAN 2.0B Controller Module
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
16-7
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 message buffer
operation, refer to
Section 16.4, “TouCAN Operation
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 operation, refer to
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
The value of the mask registers should not be changed during normal operation. If the mask register data
is changed after the masked identifier of a received message is matched to a locked message buffer, that
message will be transferred into that message buffer once it is unlocked, regardless of whether that
message’s masked identifier still matches the receive buffer identifier.
shows mask bit values.
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...
