Watlow PPC-2000 - Manual (Page 243)

PPC-2000 User’s Guide Chapter 5: LogicPro and Modbus Reference
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 215
Table 5.61 Program Version Information
Changed Data Queue
The Changed Data Queue is a tool for hosts which need to
maintain a mirror image database of the PPC-2000 database.
Typically, these are PC based hosts. Most simple operator
interfaces, such as operator interface terminals, constantly
query the PPC for only the information that needs to be
displayed on the current screen. These devices would not read
the queue.
The PPC-2000 can communicate with 1 or 2 host devices with
read/write capability. If 2 hosts are used, the changed data
queue alerts port 1 host that port 2 host has changed a
section(s) of the database and vice versa. Each port has a
dedicated queue which must be continuously monitored by the
respective host. The addresses are the same for both ports, but
the data in each queue may differ because port 1 queue
monitors port 2 activity while port 2 queue monitors port 1
activity.
The queue consists of a group of read-only registers. Register
33051 contains the quantity of parameters which have been
changed by the other host. Registers 33052-N form a first-in-
first-out stack of changed parameters consisting of the
parameter ID numbers. The queue does not report the changed
status of specific elements within a parameter but only the
parameter ID number that has been changed. Therefore, if the
changed data queue notifies host 1 that host 2 has changed a
parameter, it is necessary for host 1 to read all elements within
a parameter to update host 1's database.
Using a First In First Out (FIFO) stack, the queue logs all
changes to the database originating from another host.
Register 33052 contains the oldest change logged, 33053
contains the second oldest and so on. After the host reads the
register(s), the data is cleared and shifted in the FIFO stack.
Database Offset Description
1 Major version, first digit
2 Major version, second digit
3 Minor version, first digit
4 Minor version, second digit
5 Release level alpha character
6 Reserved
7 Reserved
8 Reserved