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Appendix B
Network Communications
Network communications are available on the Model FHC50. The Model FHC50 can
communicate with a building management system through Modbus
®
, N2, LonWorks
®
or BACnet
®
MS/TP protocols. Please refer to the appropriate section below for more detailed information.
Modbus
®
Communications
Modbus
®
communications are installed in the Model FHC50 fume hood controllers. This
document provides the technical information needed to communicate between the host DDC
system and the Model FHC50 units. This document assumes the programmer is familiar with
Modbus
®
protocol. Further technical assistance is available from TSI if your question is related to
TSI interfacing to a DDC system. If you need further information regarding Modbus
®
programming in general, please contact:
Modicon Incorporated (a division of Schneider-Electric)
One High Street
North Andover, MA 01845
Phone (800) 468-5342
The Modbus
®
protocol utilizes the RTU format for data transfer and Error Checking. Check the
Modicon Modbus
®
Protocol Reference Guide (PI-Mbus-300) for more information on CRC
generation and message structures.
The messages are sent at 9600 baud with no start bit, 8 data bits, and 2 stop bits. Do not use the
parity bit. The system is set up as a master slave network. The TSI units act as slaves and
respond to messages when their correct address is polled.
Blocks of data can be read from each device. Using a block format will speed up the time for the
data transfer. The size of the blocks is limited to 255 bytes. This means the maximum message
length that can be transferred is 255 bytes. The typical response time of the device is around
0.05 seconds with a maximum of 0.1 seconds.
Unique to TSI
The list of variable addresses shown below skips some numbers in the sequence due to internal
Model FHC50 functions. This information is not useful to the DDC system and is therefore
deleted. Skipping numbers in the sequence will not cause any communication problems. If a
variable is not used by the particular FHC50 configuration, it will be reported with a value of -1.
All variables are outputted in English units: ft/min, and cfm. If the DDC system is to display
different units, the DDC system needs to make the conversion.
Network Points
These variables can be read using Modbus
®
command 03 Read Holding Registers. They can
be written to using Modbus
®
command 06 Write Single Register. Many of these variables are
the same “menu items” that are configured from the controller keypad. The calibration and control
items are not accessible from the DDC system. This is for safety reasons since each hood is
individually setup for maximum performance.
Modbus is a registered trademark of Modicon, Inc.
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