Inter-Option Communication Timing; Cyclic Data Compression - Leroy-Somer digitax st User Manual

12.4

Inter-option communication timing

When more that one Solutions Module is fitted to a drive (not Digidrive SK),
communications between modules uses inter-option communications. Inter-option
communications is slower than the communications directly to the drive parameters.
Typical access times for direct drive menu access will be in the region of 30μs (per
parameter), a similar access using inter-option communications will be in the region of
1ms (per parameter).
When using inter-option communications, if parameters are sequential (within the same
menu) then up to six parameters may be grouped in to a block, this will take up to 1ms
for this block to be transferred. A total of eight blocks for input and eight blocks for
output are available.
12.5

Cyclic data compression

Table 12.4
Pr MM.34
By default, the SM-PROFIBUS DP-V1 uses 32-bits for each data channel, even if the
target parameter in the drive is a 16-bit parameter. This strategy (known as casting)
ensures that the cyclic data transmitted over the PROFIBUS-DP network is kept aligned
with memory locations in 32-bit PLCs. When cyclic data compression is enabled
(MM.34 = ON) a data channel will only use 32-bits if the target drive parameter is a 32-
bit parameter. If the target drive parameter is only 1, 8 or 16-bits wide 16-bits will be
used for that particular data channel. This is shown in Table 12.5.
Table 12.5 Actual data sizes
Parameter Size (bits)
1
8
16
32
The following examples demonstrate setting up a network using five cyclic channels for
both IN and OUT data with the cyclic data compression first disabled and then enabled.
SM-PROFIBUS-DP User Guide
Issue : a
Cyclic data compression enable
Default
Range
Access
Actual Data Size (bits)
Compression on
16
16
16
32
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OFF (0)
OFF (0) or ON (1)
RW
Actual Data Size (bits)
Compression off
32
32
32
32
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