wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

46-10 Industrial Communication Systems
Codename
SIL
WD_Time
F-Parameters:
Defined and constant
Identical in F-Host and F-Device
Build
CRC1
CRC1
Initial
value for
CRC2
2 Octets
FIGURE 46.16 CRC1 generation: F-Host and F-Device. (Adapted from Stripf, W. and Barthel, H., Comprehensive
safety with PROFIBUS DP and PROFINET IO—Training for “PROFIsafe certified designers.”)
Consecutive
number
Toggle bit
CRC1
Vconsnr_h
F-Output data
Control byte
CRC2
(F-Host)
Consecutive
number
(not transmitted)
0,1...0 × FFFFF
Across
F-Parameter,
F-Output data,
Control byte,
and Vconsnr_h
2 octets
3 octets
Max. 12 or 123 octets
1 octet
3 or 4 octets
CRC2
generation
FIGURE 46.17 CRC2 generation: F-Host and F-Device. (Adapted from Stripf, W. and Barthel, H., Comprehensive
safety with PROFIBUS DP and PROFINET IO—Training for “PROFIsafe certified designers.”)
46.2.9 Detected Safety Data Failures
The ultimate purpose of Profisafe is to prevent a system failure caused by an undetected communication
error. In order to determine when the system may be in a state in which there is an increasing probability
of a communication error going undetected, an SIL monitor is implemented in the F-Host. Every corrupted
message (CRC2 or virtual consecutive number fault) detected by the F-Host or F-Device will be
counted during a configurable SIL monitor time period (T). The SIL monitor time period depends upon
the SIL value of the system and the CRC2 length, which depends upon the amount of safety data being
transferred. If 12 or fewer bytes of safety data are being transferred, a 3-octet (24 bit) CRC2 is used,
© 2011 by Taylor and Francis Group, LLC