Designs, materials, weights and performance ratings are approximate and subject to change without notice. Visit
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89
Serial Communications – continued
BACnet
™
MS/TP Communications
1. BACnet MS/TP Description
The BACnet Master-Slave/Token-Passing (MSTP) driver implements a data link protocol that uses the services of the
RS-
485 physical layer. The MS/TP bus is based on BACnet standard protocol SSPC-135, Clause 9. BACnet MS/TP
protocol is a peerto-peer, multiple master protocols based on token passing. Only master devices can receive the
token, and only the device holding the token is allowed to originate a message on the bus. The token is passed from
master device to master device using a small message. The token is passed in consecutive order starting with the
lowest address. Slave devices on the bus only communicate on the bus when responding to a data request from a
master device.
2. Baud Rates on the MS/TP Bus
An MS/TP bus can be configured to communicate at one of four different baud rates. It is very important that all of
the devices on an MS/TP bus communicate at the same baud rate. The baud rate setting determines the rate at which
devices communicate data over the bus. The baud rate settings available on Armstrong Vortex Flow Meters are 9600,
19200 and 38400.
2.1. Baud Rate and MAC address configuration
1. Power on the IUT
2. Press Enter to go to the configuration menu
3. Enter the factory password 16363 (Use Up and Down arrows to enter the digits)
4. Navigate with the left arrow to Diagnostics menu
5. Press Enter and press right button immediately
6. Navigate to Config Code screen by continuous pressing down button
7. After reaching config code screen, press right to navigate to Comm. Type screen
8. Change the comm. Type to “Modbus” and press Enter
Note:
Modbus will enable Baud Rate and MAC address screens
9. Press Exit twice to go back to the Diagnostics menu
10. Navigate to Output Menu by using right or left arrow buttons
11. Press Down button and reach Baud Rate and MAC address screens
12. Change the required settings and press Exit & Enter buttons to save the configuration
13. Reboot the device by power off and on for the changes to take effect
Note:
a. IUT support 9600, 19200, 38400 baud rates
b. MAC address range is 0-127