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FX2N-32CAN Communication Module
4.2
Buffer Memory Functions
4.2.1
Data Transfer Locations, BFMs #0~#19 and #100~#199
These Buffer memory locations in the FX
transfer data to the CANbus. The mapping for where each data is sent/received is explained
in Chapter 5.
4.2.2
The Data Exchange Mode, BFM #20
On read access, BFM #20 contains a status bit for data exchange. If bit0 is "1", the module is in
data exchange mode and the received data are valid (no CAN error occurred). If bit0 is "0", the
module is not in data exchange mode.
On write access, BFM #20 acts as the data exchange control signal. To ensure that the FX
32CAN module can handle the PDO data in a consistent way, it is absolutely necessary to
write a "1" to this BFM before reading Rx PDO data (FROM) and after writing Tx-PDO data
(TO) to the module. The data exchange control signal ensures, by internal buffer exchange,
that TO data from the PLC will be transmitted within the same corresponding Tx-PDO at the
same time.
TO data will only be sent to the CAN bus after a write access to BFM #20 (data = 1).
As long as the reading of the previous data is not finished and a new exchange command to
BFM #20 has not been sent, FROM data from the CAN bus will not be (partially) overwritten by
further Rx PDOs with the same ID.
If the CAN open module is in data exchange mode, the received PDO data (Rx-PDO) from
other nodes can be read by the FX
transmit PDO data (Tx-PDO) can be written to the module and sent to the network by using a
TO instruction.
-32CAN module are used to receive from and
2N
/FX
PLC by using a FROM instruction and the
2N(C)
1N
Buffer Memory Structure 4.
4-2
-
2N
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