Rockwell Automation 57C445 AutoMax PC Link Interface Module - Manual (Page 40)

D2Ć5
2.3.2 Drop 1Ć55 Register Definitions
The register definitions for drops 1Ć55 can be summarized as follows:
Registers 0 through 31 contain 32 words of output (to the Master).
These registers are read/write if the module is actively responding as
this drop; otherwise, these registers are read only.
Registers 32 through 63 contain 32 words of input (from the Master).
These registers are read only.
2.4 Data Change Table (DATA_CHNGE)
The data change table contains one byte for each drop. Drop 0
corresponds to the first location in the table (1f00h). The RENET
software places 0xFF in the data change table for a particular drop
any time data in the drop changes (other than that written by the
host). The data change byte for drop 0 is affected only by changes to
the broadcast data registers (32Ć39).
Rather than poll drops continuously, a host application may check
the DATA_CHNGE flag for a given drop. If it is zero, no data in the
drop has changed and the host may proceed accordingly. If the data
change flag is set to 0xFF, the host then clears the flag to zero, and
reads the updated data for the drop.
2.5 Status Change Flag (STAT_CHNGE)
This flag is set to 0xff by the RENET software if any data in the drop
status registers change (registers 4Ć7 of drop 0). Any change to these
registers indicates that one or more drops have gone on/off line.
Rather than monitor the drop status bits continuously, the host need
only monitor the STAT_CHNGE flag. If it is zero, no drops have gone
on or off line, and the host may proceed accordingly. If the status
change flag is set to 0xFF, the host then checks the relevant bits in
the drop status registers (registers 4Ć7 of drop 0).
2.6 Global Change Flag (GLOB_CHNGE) and
Enable Global Change Table
(EN_GLOB_CHNGE)
The Global Change flag is used in conjunction with the Enable
Global Change Drop Table to provide a flag which is set only when
data in selected drops changes. The global change flag will also be
set if the status changes (See section 2.5 of this appendix).
For example:
A particular application needs only to monitor drops 0, 3, and 7.
The host places 0xff in the EN_GLOB_CHNGE table for drops 0, 3,
and 7 at locations 0x1F40, 0x1F43, and 0x1F47. The GLOB_CHNGE
flag will be set any time data in any of the given drops changes.
The host needs to monitor the GLOB_CHNGE flag only. If it is set, the
host clears it to 0. The host then checks the status change flag and
the data change flags for the given drops and proceeds accordingly.