ALSPA PROFIBUS Field Bus Coupler
7. Menu 74 Parameters
(09/06)
Technical Manual
Page 7-7
If a loss of PROFIBUS reference is declared, (see Section 7.4.8)
the reference value will no longer be updated by the PROFIBUS
link. In this situation the user has the choice of using the last value
obtained from the PROFIBUS link or using the fallback value.
Each reference has an associated fallback value that will be copied
into the reference value as soon as a loss of PROFIBUS event
occurs. Fallback copying only occurs if the freeze/fallback
parameter is set to fallback.
The fallback value will be valid until the PROFIBUS network
recovers, at which time the PROFIBUS data will be used.
Be aware that the fallback mechanism only applies to values in the
even numbered parameters between P74.20 to P74.42. Received
data transferred directly to Drive parameters will not have the
fallback option but will freeze on loss of the network – refer to the
block diagram at the end of this manual.
Note also that all fallback parameters will be copied to their partner
parameter whether or not the parameter is in use.
Table 7-2 illustrates the relationship between the received PPO
word and the parameter pointers and reference "holders"
(destination parameters) – refer also to the block diagram.
Table 7-2 Received PPO data mapping example for PPO type 4
PPO Reference
Parameter Pointer
Holder
(Destination Parameter)
PZD1 (STW)
P74.50
=
74.40
PZD2 (HSW)
P74.52
=
74.20
PZD3 P74.54
=
74.22
PZD4 P74.56
=
74.24
PZD5 P74.58
=
74.26
PZD6
P74.60
=
74.28 or 74.42
Entering a value of 0 in a pointer parameter will mean that any data
associated with that parameter is ignored, as P0.00 is not a valid
parameter.
