YSI WaterLog Series, Owner'S Manual

Page: 109 / 174

Configuring Modbus Registers
After selecting a Modbus setup, the Modbus Master/Slave Properties screen will appear. The
port and Modbus registers are primarily displayed on the Modbus Properties screens. Modbus
Slave setups allow additional Tasks to be added or removed from the setup. The Properties
screen may contain a few extra options dependent on where the screen was accessed.
Modbus registers have many customizable options including the register’s address, which table it
table it resides in, as well as the number type. Modbus registers can be edited by pressing the
corresponding Edit button.
Register Address: Defines the register(s) associated with the given Task. If a Task is an Input,
the value found in the given register(s) will be read each scan. If the Task is an Output, the value
of the Task will be written to the register(s) each scan.
Register addresses begin numbering at 1. Some Modbus Masters and Slaves, however, retrieve
registers starting at address zero. An offset of one should be used in those cases. For example,
to retrieve the value at address zero of a PLC acting as a Modbus Slave, a Modbus Master Input
could be used by setting the register address to one.
Table: Defines which Modbus table the selected register is a part of. Only corresponding
function codes can retrieve registers from the selected table. Typically Holding Registers or
Input Registers are used for reading and writing values in Modbus. Multiple registers can be
assigned with these tables by changing the Number Type. Discrete Input and Coil can only
contain a 1 or 0 value and are generally associated with either a digital port or a true/false
condition.
System 5000
Modbus 8-5
TM