MPC555CME Freescale Semiconductor, MPC555CME Datasheet - Page 597

• Manufacturer Part Number: MPC555CME
• Description: KIT EVALUATION FOR MPC555
• Manufacturer: Freescale Semiconductor
• Type: Microcontrollerr

Specifications of MPC555CME

• Contents: Module Board, Installation Guide, Power Supply, Cable, Software and more
• Processor To Be Evaluated: MPC555
• Data Bus Width: 32 bit
• Interface Type: RS-232
• For Use With/related Products: MPC555
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

16.4.4.2 Locking and Releasing Message Buffers
16.4.5 Remote Frames
MPC555
USER’S MANUAL
Data must never be written into a receive message buffer. If this occurs while a mes-
sage is being transferred from a serial message buffer, the control/status word will re-
flect a full or overrun condition, but no interrupt is requested.
The lock/release/busy mechanism is designed to guarantee data coherency during the
receive process. The following examples demonstrate how the the lock/release/busy
mechanism affects TouCAN operation.
Polling the control/status word of a receive message buffer can lock it, preventing a
message from being transferred into that buffer. If the control/status word of a receive
message buffer is read, it should be followed by a read of the control/status word of
another buffer, or by a read of the free-running timer, to ensure that the locked buffer
is unlocked.
The remote frame is a message frame that is transmitted to request a data frame. The
TouCAN can be configured to transmit a data frame automatically in response to a re-
mote frame, or to transmit a remote frame and then wait for the responding data frame
to be received.
To transmit a remote frame, the user initializes a message buffer as a transmit mes-
sage buffer with the RTR bit set to one. Once this remote frame is transmitted success-
fully, the transmit message buffer automatically becomes a receive message buffer,
with the same ID as the remote frame that was transmitted.
1. Reading a control/status word of a message buffer triggers a lock for that
2. To release a locked message buffer, the CPU either locks another message
3. If a receive frame with a matching ID is received during the time the message
4. When a locked message buffer is released, if a frame with a matching identifier
5. If two or more receive frames with matching IDs are received while a message
6. If the user reads the control/status word of a receive message buffer while a
/
MPC556
message buffer. A new received message frame which matches the message
buffer cannot be written into this message buffer while it is locked.
buffer by reading its control/status word or globally releases any locked
message buffer by reading the free-running timer.
buffer is locked, the receive frame is not immediately transferred into that mes-
sage buffer, but remains in the serial message buffer. There is no indication
when this occurs.
exists within the serial message buffer, then this frame is transferred to the
matching message buffer.
buffer with a matching ID is locked, the last received frame with that ID is kept
within the serial message buffer, while all preceding ones are lost. There is no
indication when this occurs.
frame is being transferred from a serial message buffer, the BUSY code is indi-
cated. The user should wait until this code is cleared before continuing to read
from the message buffer to ensure data coherency. In this situation, the read of
the control/status word does not lock the message buffer.
CAN 2.0B CONTROLLER MODULE
Rev. 15 October 2000
MOTOROLA
16-15