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3
ModBus Confi guration
Timing Specifi cations
Th e baud rate for the ModBus board is selectable with Dip
switch #9.
1 = 19200 bps
0 = 9600 bps
Each message is started by at least 3.5 character times of
silence. Th e maximum delay between frames is 1.5 character
times.
When the system temperature, tank temperature, and/or
0-10V BMS voltage is provided by the BAS to the boiler, it
is critical that the values be updated every few seconds. If
the boiler does not receive updated values within a timeout
period (installer adjustable), the control will revert to using its
own readings (if connected). Th e timeout is programmable
as follows:
Please note that the brackets ([]) denote
NOTICE
screen status.
1.
Press and hold the LEFT SELECT [MENU] key for 5
seconds.
2.
Enter installer code - 5309.
3.
Scroll down and select [CONTROL MODES].
4.
Scroll down and select [MODBUS T/O].
5.
Scroll to desired time. Press the RIGHT SELECT [SAVE]
key.
Th e timeout is adjustable between 5 and 120 seconds. Th e
default timeout is 10 seconds.
When the BAS is not providing any of these values, but
is still controlling the boiler (such as providing an enable
command), the BAS must refresh these commands at least
every 4 minutes. If the commands are not refreshed, the
boiler will revert to operating based on its own inputs.
Parity
Parity is set by the position of Dip switch #10.
0 = No Parity
1 = Even Parity
If No Parity is selected there will be two stop bits, otherwise
there will be one.
8
ModBus and BACnet Communication Instructions
Data Transmission Mode
Many ModBus bus master devices can be confi gured to
transmit data in either ModBus RTU or ModBus ASCII modes.
Since RTU messages can be formatted to use fewer data bits and
are therefore more effi cient, RTU has been chosen to be used
with all Lochinvar ModBus communication. Please ensure that
the master device is transmitting ModBus RTU.
ModBus Board Diagnostics
Th e ModBus board is equipped with three LED's for visual
diagnostics: Two yellow LED's and one green. One yellow LED
(D5) is used to indicate transmission of data. Th e other yellow
LED (D6) is used to indicate reception of data. Th e green LED
(D7) is used to show internal faults.
Internal Faults:
Normal Operation = 1 second bright, 1 second dim
Controller Fault = Continuously on
No Burner Control Communication = 0.5 seconds on, 1.5
seconds off
No ModBus Communication = 1.5 seconds on, 0.5 seconds
off
ModBus Communication
Th e ModBus communication commands and exception codes
that are supported by the ModBus communication board can
be found on pages 8 and 9 of this manual.
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