GE PACSystems RX7i, Руководство пользователя

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Chapter 4. Configuration
56 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
The “Produce in Backup Mode” parameter appears in the properties for each produced exchange.
Figure 32: Configuring Produce in Backup Mode Parameter
Using Signatures in Ethernet Global Data
EGD signatures can be used to make sure that the format of the data from the producer matches that
expected by the consumer.
The EGD signature is a numeric value that has two parts: the major number and the minor number. The major
number reflects the “primary format” of the data. The minor number reflects backward-compatible changes
made to the EGD exchange (such as adding data to the end of the exchange). An EGD signature has the format
maj.min
, where
maj
is the major value and
min
is the minor value.
The primary format of the data is first established when the EGD exchange is defined. At that time the signature
is assigned the value of 1.0. Any change that reorders, removes, renames or changes the type or offset of a
variable in the exchange is a primary format change that causes the signature major number to be
incremented. The signature major number must match between the producer and the consumer for the
consumer to consume the data. Packets that are received when produced and consumed exchange signatures
are enabled and incompatible (different major signature values) will result in an error consumed exchange
status.
The signature minor number is incremented when backward-compatible changes are made in the format of
the produced data. Backward-compatible changes are made by adding data to unused areas of the exchange
including adding data to the end of the exchange. After checking the signature major number, the consumer
checks the signature minor number. If the signature minor number in a sample is greater than the signature
minor number configured for the exchange in the consumer then the consumer can consume the data
truncating any unexpected data at the end of the sample. The consumer can do this because the minor
number change guarantees that only backward-compatible changes have been made in the format of the
data.
If the signature of a produced exchange is specified as zero, then consumers will not check it. If the signature of
a consumed exchange is configured as zero, then any signature from a producer will be accepted and the data
used if the length of the data exactly matches the expected length.
Only the PACSystems RX7i and RX3i support non-zero signatures. All other targets force the signature for both
produced and consumed exchanges to be zero.