Fujitsu FR81S User Manual
CHAPTER 41: CAN
5. Operation
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER
: CAN
FUJITSU SEMICONDUCTOR CONFIDENTIAL
62
5.1.2. Data Transmission/Reception with Message RAM
Data transmission/reception with message RAM is shown.
The BUSY bit of the IFx command request register (IFxCREQ) will be set to "1" when the data transfer
between the message interface register and message RAM is started. The BUSY bit will be cleared to "0"
after the transfer completion (see Figure 5-1).
The IFx command mask register (IFxCMSK) sets whether to transfer the entire or partial data of a message
object. Due to the structure of message RAM, it is not possible to write a single bit/byte of the message
object to message RAM. The entire data of a single message object is always written to message RAM.
Data transfer from the message interface register to message RAM therefore requires a read-modify-write
cycle.
Figure 5-1 Data Transfer between Message Interface Register and Message RAM
Start
Writing to the IFx command
request register
BUSY = 1
Interrupt = 0
BUSY = 0
Interrupt = 1
WR/RD = 1
Reading from the message RAM
to the message interface register
Reading from the message RAM
to the message interface register
Writing to the message RAM
from the message interface register
No
No
Yes
Yes
MB91520 Series
MN705-00010-1v0-E
1755