GE PACSystems RX7i, User Manual

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Chapter 4. Configuration
GFK-2224Q January 2017 65
Double-clicking on the consumed exchange opens a window for this exchange for configuring the variables
within the exchange. Each exchange has its own variable list. These variables contain the data that is
consumed from the network. Each variable contains the following information
Offset
(Byte.Bit)
The location within the data area for this exchange where the start of this data for this
variable is located. The offset is expressed as Byte.Bit , where
Byte
is a zero-based byte
offset and
Bit
is a zero-based bit position within that byte. (Valid bit values are 0-7. Bit 0 is
the least-significant bit within the byte; bit 7 the most significant.)
Variable The name defined for this variable.
Ref Address The PLC memory reference address that contains the start of the data for this variable. For
consumed exchanges, %S memory types and override references are not allowed. (This field
is non-editable when the Ignore selection is set to True.)
Ignore
Allows consumer to ignore this variable. Setting Ignore to True means this variable is not
sent to the PLC reference table. Defaults to False.
Length Size of the data for this variable, expressed in units of the selected PLC reference memory
type.
Type Data type of the selected PLC reference memory type. (Automatically setup by the Ref
Address selection.)
Description An optional text description of this variable.
To add a new variable to the end of the exchange, click the ‘ Add’ button. This does not change the data offsets
of any existing variables within that exchange.
To insert a new variable among the existing variables, click on an existing variable. When you click the ‘
Insert’
button, a new variable will be created ahead of the selected existing variable. This changes the data offsets of
all subsequent variables in the exchange.
Once a new variable has been entered, double-click a data field within the row to edit that value.
To delete an existing variable, click on the variable row and then click the ‘
Delete ’ button.
The sum of all variables in the exchange must not exceed 1400 bytes. The total length of the exchange (in
bytes) is displayed as ‘ Length (Bytes): ’ at the top of the exchange window above the variable list. PACSystems
CPUs with firmware version 5.0 and later support a maximum of 30,000 variables for all exchanges. Earlier
firmware versions support approximately 12,000 variables total for all exchanges.
A variable is automatically created for the required Status variable. This variable contains the local exchange
status that is returned to the PLC logic application. The exchange status is not part of the consumed exchange
data.
A variable is automatically created for the optional Timestamp variable. This variable contains the timestamp of
the last received data packet (generated when the exchange was produced) that is returned to the PLC logic
application. Set the Ref Address to NOT USED to ignore the timestamp variable.
Any consumed data variable may be ignored by setting the Ignore selection to True. See Selective
Consumption, below.
Note: If the total data length of a consumed exchange does not match the length of the produced exchange
received from the network, PLC Faults and Ethernet exceptions will occur.