Register Configuration - GE 90*-30 PLC Series User Manual

4

Register Configuration

The area in the center of the Module Configuration screen is used to configure and
monitor the register definitions for the module. During the initial module definition
phase the only parameters that need attention are the maximum sizes and the start
addresses. The other fields will be automatically updated as network variables are
defined.
The maximum sizes begin as default values based on the choice of CPU type (see above).
The default register size defaults to the maximum register size for the chosen CPU or the
maximum size based on the network variable capacity of the LBIM. The LBIM can use
up to 240 network variables, so the maximum for the discrete registers would be 240
discrete locations for network variables. Additionally, the %I register is where the valid
bits for all network variables are stored. For a configuration using 240 %I references,
there are 240 bits plus 240 valid bits plus 8 reserved bits for a total of 488 possible %I
references.
The maximum size definition is only for configuration error checking purposes and can
be changed later if necessary. Defaults for the various CPU types can be changed by the
user (see Default Button command below).
The Start Addr fields allow the user to define any valid beginning reference value for the
individual registers. This start definition is relative to the configured start address as
defined for the module in the PLC backplane. This allows two or modules to use
identical module configurations and be configured into the same PLC backplane with
differing address ranges. For example, if two modules had identical configurations with
%I starting at address 1 with length 100, they could be configured into the same
backplane using Logicmaster software as foreign modules with start addresses in %I of 1
and 101 respectively. The PLC program then addresses the variables in the two modules
using references that are offset by 100 from each other.
The Entries field is for monitoring only and shows the number of variables currently
defined for that particular register. The Length field is for monitoring only and shows
the total length of the defined register space. This value includes gaps left between
variables as the register configuration must be contiguous. The graphical usage display
shows a bar graph representation of the defined variable space versus the maximum
defined space.
4-8 Series 90™-30 PLC LONWORKS® Bus Interface Module User's Manual – June 1997 GFK-1322A