Curtis 1356/1356P CAN Expansion Module Manual,
Rev. A
25
USING AN SDO TO MAP A PDO
The following SDO format shows how to map an SDO to a PDO.
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Request
LSB
MSB
Sub-
LSB Index MSB Index Sub-index Length
WR
Index
Index
Index
of Object of Object of Object
Byte 1 contains the request “Write” action, as described earlier.
Bytes 2 through 4 describe the PDO and the byte within the PDO that
is to be mapped. Bytes 2 and 3 hold the index indicating the PDO and Byte
4 holds the sub-index (range 1–8) indicating the PDO byte to be mapped.
Bytes 5 through 8 describe the object to be mapped; in other words; they
define the object that has the data that will be transmitted. The object index
comes first (least significant byte first), followed by the sub-index, followed by
the number of bits to be transferred (must be 8). Note that the sub-index here
is used to specify a particular byte within a multi-byte object.
For example, take a 32-bit object. To access the least significant byte of
a long word (32 bits), the sub-index should be set to 0. To access the most
significant byte of a long word (32 bits), the sub-index should be set to 3.
The SDO commands below show an example of mapping the encoder
pulse counts (32 bit, index=0x3190) to PDO1-MISO bytes 1–4.
Map the LSB byte to PDO1-MISO Byte 1
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
0x22 0x00 0x1A 0x01 0x90 0x31 0x00 0x08
Map the second byte to PDO1-MISO Byte 2
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
0x22 0x00 0x1A 0x02 0x90 0x31 0x01 0x08
Map the third byte to PDO1-MISO Byte 3
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
0x22 0x00 0x1A 0x03 0x90 0x31 0x02 0x08
Map the MSB byte to PDO1-MISO Byte 4
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
0x22 0x00 0x1A 0x04 0x90 0x31 0x03 0x08
In these SDO commands, bytes 2 and 3 hold the index of PDO1_MISO
mapping (0x1A00) and the sub-index in byte 4 shows the byte to be mapped.
Bytes 5 and 6 hold the object index (0x3190) and the sub-index in byte 7 shows
the byte in the 32-bit object to be mapped.
5 — SDO: Communication Profile Objects
Summary of Contents for 1356
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