Installation and Operation Guide | DGS Modbus
© Danfoss | ADAP-KOOL® | 2016.12
12 | RS8HJ102 |
Modbus connection
Connector CN4 (labeled G, +, and -) is an RS-485 port for communicating with DGS Modbus gas detec-
tors in Modbus-RTU protocol.
Modbus Address
To establish Modbus communication to Danfoss front end, configure the address using SW1 and SW2
and perform a network scan from the front end.
The Baud rate may need changing. It must be set to 19,200 baud when used with AK-SM 720/AK-SM
350 and when AK-SM 800 is configured in SLV-mode (see manual for AK-SM 800 for further details).
As default the AK-SM 800 communicate at the same baudrate as DGS.
The Hexadecimal Address Switches are used to set a unique address for the sensor. Valid addresses are
0-247.
The Modbus address can be set by the combined settings on the hexadecimal dial switches SW1 and
SW2. Addresses 0-15 are selectable with switch SW1 (the least significant portion of the address). SW2
scales the addresses by a factor of 16 (the most significant portion of the address).
ADDR = 16 x SW2 + SW1
Example: 40 = 16 x 2 + 8
SW1 = Least Significant Hex Character (0-F) = 0-15
SW2 = Most Significant Hex Character (0-F) = 0-15
ADDR
SW2 SW1
1 0 1
2 0 2
3 0 3
: : :
9 0 9
10
0 A
11
0 B
: : :
15
0 F
16
1 0
: : :
246
6 F
247
7 F
See appendix B for complete list of all address'
NOTE
: Addresses 0 and 248-255 (0x8F – 0xFF) are reserved.
Baud rate
To choose a Baud rate, select the address and reset the gas detector by temporarily shorting jumper J4
(or by cycling the power off and on). After the Baud rate is set, the desired Modbus address (1-247) can
be selected by changing the switch settings with a power-cycle or reset operation afterwards.
Addresses 253 (0xFD) to 255 (0xFF) are reserved for setting the Modbus communications Baud rates.
ADDR
S2 S1 BAUD
RATE
254
F
E
9,600
255
F F 19,200
253
F
D
38,400 (Default)
NOTE:
The default Baud rate is 38,400.
CAUTION
4.4 System integration
G
Ground
(Galvanically separated)
+
Non-inverting
Modbus Signal (A)
TxD+/Rxd+
-
Inverting
Modbus Signal (B)
TxD-/Rxd-
