CAN-8123/CAN-8223/CAN-8423 user’s manual (Revision 3.00, May/22/2009) ------
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There shall be up to 4 TxPDO mapping objects and up to 4 RxPDO
mapping objects with default mappings.
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The 1st RxPDO and TxPDO mapping objects are used for digital
outputs and inputs to each other.
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The 2nd, 3rd, and 4th RxPDO and TxPDO mapping objects are
respectively assigned to record the value of analog outputs and
inputs.
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If a device supports too many digital input or output channels over 8
channels, the related analog default PDO mapping objects remaining
the additional unused digital I/Os will use its additional objects. This
rule with the same concept is used on the additional analog channels.
Take the RxPDO as an example; there are 11 DO and 13 AO object
entries in the object dictionary. Generally in the CAN-8123 /
CAN-8223 / CAN-8423, the first 8 DO object entries will be mapped to
the first RxPDO mapping object because one DO object entry needs
one byte space. The last 3 DO object entries will be assigned to the
5th
RxPDO according to the above rules the 2nd and the 3rd.
Furthermore, one AO object entry needs 2 bytes of space. Therefore,
the second RxPDO mapping object has been occupied by the first 4
AO object entries. The following 4 AO object entries will be assigned
to the third RxPDO mapping object, as well to the 4th RxPDO
mapping object. Because the 5th RxPDO mapping object has been
occupied by the DO object entries, the last AO object entry shall be
assigned into the 6th RxPDO mapping object.
Before applying the PDO communications, the PDO producer and the
PDO consumers must have mutual PDO mapping information. On the one
hand, the PDO producers need PDO mapping information to decide how to
assign the expected practical I/O data to PDO messages. Besides, PDO
consumers need the PDO mapping information to recognize each byte of
received PDO message, i.e. when a PDO producer transmits a PDO object to
PDO consumers, the consumers will contrast this PDO message with PDO
mapping entries, previously obtained from the PDO producer, and then
interpret the meanings of these values from the received PDO object. For
example, if a CANopen device has 16 DI, 8 DO, 2 AI, and 1 AO channels. The
input or output values of these channels will be mutually stored into several
specific entries.
