Sdo Communications; Sdo Master Request, Sdo-Rx (Mosi) - Curtis 1352 Manual

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Curtis 1352 eXm Manual,

SDO COMMUNICATIONS

CANopen uses Service Data Objects (SDOs) to change and view all internal
parameters, or "objects." The SDO is an 8-byte packet that contains the address
and sub-address of the parameter in question, whether to read or write that
parameter, and the parameter data (if it is a write command). SDOs are sent
infrequently and have a low priority on the CAN bus.
SDOs are designed for sporadic and occasional use during normal runtime
operation. There are two types of SDOs: expedited and block transfer. The eXm
does not support large file uploads or downloads (using the block transfer), so
all SDOs in this specification are expedited SDOs.
The SDOs in the eXm are used to set up and parameterize the module.
They are also used to retrieve basic module information (such as version or
manufacture date), review the fault log, and monitor a few key internal variables
(mostly for system debug purposes).

SDO Master Request, SDO-RX (MOSI)

An SDO transfer always starts with a request message from the master. Each
SDO request message consists of one control byte, a two-byte CAN Object
index, a one-byte CAN Object sub-index, and up to 4 bytes of valid data. This
format is CANopen compliant.
SDO-MOSI (RX)
Byte 1 Byte 2
Control
The first data byte contains R/W message control information.
Action
Read
Write
The next two data bytes hold the CAN Object index. The least significant
byte of the index appears first, in byte 2, and the most significant byte appears
in byte 3. For example, if the index is 3021h, byte 2 holds the 21h and byte 3
holds the 30h.
Data byte 4 holds the CAN Object sub-index. When there is only one
instance of a parameter or value type, this value is 0. If there are several related
parameters or values, the sub-index is used.
The last four data bytes hold the data that is to be transferred. In the case
of a single-byte transfer, the data is placed into data byte 5, with bytes 6 through
8 being undefined (set to 0). In the case of a 16-bit transfer, the lower 8 bits
appear in data byte 5 and the upper 8 bits appear in data byte 6; bytes 7 and 8
are undefined (set to 0). The case of a 32-bit transfer follows the same strategy,
Rev. D
(received from the system master)
Byte 3 Byte 4
CAN Object Index Sub-index
Byte 1
Value
42h
22h
5 — SDO COMMUNICATIONS
Byte 5 Byte 6 Byte 7
Data Data Data
Byte 8
Data
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