MSM9225B User’s Manual
Chapter 2 Register Descriptions
2 – 6
(6) Transmission request: TRQ
When a message box is used for transmission, write “1” to this bit from the microcontroller. When
transmission ends normally, “0” is written to this bit. This means that the TRQ bit is “1” during
transmission. Therefore, to request transmission, confirm that the TRQ bit is “0” first, and then write “1”
to the TRQ bit. Set the TIRS bit of CANC to start transmission.
When the remote frame is received while the ARES bit is “1”, the TRQ bit is set to “1”.
At reset, the TRQ bit is set to “0”
(7) Overwrite flag: OW
When the RCS bit is “1”, this bit is set to “1” if data has been received by the same message box again.
That is, OW is a flag to indicate that receive data has been overwritten.
At reset, the OW bit is set to “0”.
(8) Message box access request/enable bit: MMA
Be sure to write a “1” to the MMA bit before writing to a message box from the microcontroller. Then
read the MMA bit. If “1” is read, the message box is accessible. If “0” is read, write a “1” in a loop
until the MMA bit actually becomes “1”.
After a “1” has been written to the MMA bit and the message box has been rewritten, be sure to write a
“0” to the MMA bit. Then read the MMA bit. If “1” is read, write a “0” in a loop until the MMA bit
actually becomes “0”.
The initialization bit INIT of the CAN control register (CANC: 0Ehex) has priority over the MMA bit.
That is, when INIT is “1”, the MMA bit is read as “1” irrespective of whether the MMA bit content is
“0” or “1”, so that the message box becomes accessible. In addition, after INIT is reset to “0”, all the
MMA bits will be set to “0”.
At reset, the MMA bit is set to “0”. It is possible to rewrite the contents of the other bits in the message
control register (MCR) at the same time that the MMA bit is overwritten.
When the MMA bit of a message box is set to “1”, do not set the MMA bit of other message box to “1”.
B
Summary of Contents for MSM9225B
Page 7: ...Chapter 1 Overview...
Page 13: ...Chapter 2 Register Descriptions...
Page 53: ...Chapter 3 Operational Description...
Page 62: ...Chapter 4 Microcontroller Interface...
Page 71: ...Chapter 5 Electrical Characteristics...
Page 81: ...Appendixes...