Watlow PPC-2000 - Manual (Page 187)

PPC-2000 User’s Guide Chapter 5: LogicPro and Modbus Reference
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 161
The cells in the database tables are referred to as registers.
There are two types of registers in the database: bit registers
and word registers. Bit registers hold a single bit and word
registers hold 16-bit integers.
These registers may be accessed by software running on a PC
or by an operator interface terminal or by a logic program
running on the PPC itself. Some parameters are read only, but
others may be read or changed.
Data Table Organization
The datatable is organized according to the Modbus standard
for PLC memory. Memory is divided into four sections by size
and function. The Modbus specification allows for up to 9,999
registers for each section. Some registers are not available in
the PPC-2000. Consult the parameter tables in this chapter to
determine which registers are available. Also, the usage of
some registers in the PPC-2000 differs from standard PLC
usage; for instance, coils are used for digital input status.
Coils
Coils are bit registers. Each have a value of 1 or 0. Software
interfaces may read or write the values stored in these
registers. The modbus addresses for Coils range from 0001 to
9999 (decimal).
Inputs
Inputs are bit registers. Each has a value of 1 or 0. Software
interfaces may read but not write the values stored in these
registers. The modbus addresses for Inputs range from 10001
to 19999 (decimal).
Holding Registers
Holding registers are 16-bit size; they store values from
-32,768 to 32,767. Software interfaces may read or write the
values stored in these registers. Some of the PPC-2000
parameters stored in holding registers have more limited
ranges than the register size. The modbus addresses for
holding registers range from 40001 to 49999
Input Registers
Input registers are 16-bit in size; they store values from
-32,768 to 32,767. Software interfaces may read but not write
the values stored in these registers. The PPC-2000 uses these
registers to store analog and encoder input values. The Modbus
addresses for the input registers range from 30001 to 39999.