Chapter 6 – Communications
TestEquity 101H Temperature/Humidity Chamber
Page 59
Modbus
The F4T controller is equipped with Modbus® TCP as an embedded protocol.
Introduction to the Modbus Protocol
Modbus provides the advantage of being extremely reliable in exchanging information. This
protocol works on the principle of packet exchanges. The packet contains the address of the
controller to receive the information, a command field that says what is to be done with the
information, and several fields of data. Each parameter has a unique Modbus register number.
All Modbus registers are 16-bits and are listed in the following table as relative addresses
(actual). Some F4T parameters are contained within 32 bits (IEEE Float, signed 32 bit). Notice
that only one (low order) of the two registers is listed on the next page. By default, the low order
word contains the two low bytes of the 32-bit parameter. As an example, in the table below see
Actual Chamber Temperature. Note that it lists register 27586. Because this parameter is a float,
it is actually represented by registers 27586 (low order bytes) and 27587 (high order bytes). The
Modbus specification does not dictate which register should be high or low order therefore, the
controller provides the user the ability to swap this order.
F4T and F4 Modbus Mapping
For making an easy transition from the F4 to the F4T controller using Modbus, a special set of
the most commonly used F4 registers were created. Notice that there are two tables of Modbus
registers, they are unique sets of registers (not interchangeable) and the user must select one set
or the other when implementing using Modbus.
•
Map 1 = F4T registers (default)
•
Map 2 = Limited set of F4 compatible registers (for compatibility with software written for
the F4)
To change the Modbus mapping using the F4T front panel:
1.
From any screen, press the
Menu
button
2.
Press the
Settings
button and then the
Network
button
3.
Select the
Ethernet
(for LAN) or
Modbus
(for RS-232) communications channel
4.
Scroll the screen down to find
Data Map
and select
1
(for F4T) or
2
(for legacy F4
Compatibility Mode).
5.
Recycle the power to put the new settings into effect.
