5.3 Modbus RTU interface
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Expansion module EM-BAC-MOD-01 XAC
When used in the X-AIRCONTROL base device
Communication via Modbus RTU
Switches and status LEDs
Green LED, illuminated: Power is being supplied to the device.
Green LED, blinking: Data is being received via Modbus.
Red LED, flashes: Modbus transmission error.
Slide switch: Used to switch between Modbus and BACnet.
Rotary switches: Used to set device addresses (Modbus slave address).
Valid addresses are 01-99; devices with one of these addresses can communicate
via Modbus. Address 00 is reserved for broadcast; a device with this address can
receive, but not send data.
The dip switch is used to set the operating mode:
Switch 2
OFF ON OFF ON
Switch 3
OFF OFF ON ON
Baud rate 9600 19200 38400 57600
Switch 5
OFF ON OFF ON
Switch 6
OFF OFF ON ON
Parity
none none odd even
Switches 1,4,7 and 8 have no function.
If you change a switch setting, the device will be reset after about 1 s and
restarted with the new setting.
Frame timing with Modbus RTU
Modbus frames are separated by gaps, or intervals. The following intervals apply
to rates of up to 19200 Bd; values for higher Baud rates are given in brackets:
- Send process: A maximum of 1.5 character times (750µs) is considered an
interval between 2 characters of a frame.
- Send process: An interval between 2 frames must be at least 3.5 character
times (1750µs).
- The range between these values is considered a tolerance range by the
recipient.
If this interval is exceeded during a send process, the frame ends.
This module sends messages (characters) continuously, i.e. without intervals.
There is a silent interval of >= 3.6 character times (1800µs) before the send
process starts.
A receive process ends after an interval of about 2.5 character times (1250µs).
Configuring interfaces to the central BMS
Modbus RTU interface
Single room control system FSL
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CONTROL II
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