Festo SEC-AC-305-CO, Manual

Page: 43 / 272

4. Access methods/SDO access
4−5
Festo P.BE−SEC−AC−CO−E N en 0802a
4.2 Access by SDO
The object dictionary can be accessed with
S
ervice
D
ata
O
b
jects (SDO). This access is particularly easy and clear. There
fore it is recommended to base the application on SDOs first
and later adapt some accesses to the certainly faster but
more complicated Process Data Objects (PDOs).
SDO accesses always start from the superimposed control
(host). The host sends a write request to change a parameter
or a read request to get a parameter from the servo con
troller. Every request will be answered by the servo controller
either sending the requested parameter or confirming the
write request.
Every command has to be sent with a definite identifier so
that the servo controller knows what command is intended
for it.
This identifier is composed of the base 600
h
+ node
number of the corresponding servo controller. The servo
controller answers with identifier 580
h
+ node number.
The structure of the writing and reading sequences depends
on the data type as 1, 2 or 4 data bytes have to be sent or
received. The following data types will be supported:
UINT8 8 bit value, unsigned 0... 255
INT8 8 bit value, signed −128... 127
UINT16 16 bit value, unsigned 0... 65535
INT16 16 bit value, signed −32768 ... 32767
UINT32 32 bit value, unsigned 0... (2
32
−1)
INT32 32 bit value, signed −(2
31
) ... (2
31
−1)