Network Communications; Unique To Tsi; Appendix B; Modbus Communications - Pressura RPM10 Operation And Service Manual

Appendix B

Network Communications

Network communications are available on the PresSura room monitors. The PresSura room
monitors can communicate with a building management system through Modbus
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BACnet MS/TP protocols. Please refer to the appropriate section below for more detailed
information.
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Modbus Communications
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Modbus communications are installed in the PresSura room monitors. This document provides
the technical information needed to communicate between the host DDC system and the
PresSura room monitors. 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
general, please contact:
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The Modbus protocol utilizes the RTU format for data transfer and Error Checking. Check the
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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
PresSura room monitors 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 PresSura room monitors, 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.
Modbus is a registered trademark of Modicon, Inc.
Modicon Incorporated (a division of Schneider-Electric)
One High Street
North Andover, MA 01845
Phone (800) 468-5342
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, LonWorks or
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programming in
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