GB
MSA OPERATION
ULTIMA
®
X
3 TM
17
4.3. ModBUS Communications
The communications protocol is ModBUS RTU over an RS-485 hardware
network. The default settings for communications parameters are 19200 baud
and even parity. The stop bits are fixed at 1 stop bit. For data types that are larger
than one word, the most significant word is located in the first register (big-
endian).
4.4. Supported ModBUS Function Codes
Function number Description
3
Read Holding Registers
5
Write Single Coil
6
Write Single Register
16
Write Multiple Registers
4.5. ModBUS Memory Map Overview
The ModBUS port allows for access to a significant amount of information which
may be necessary for your system integration requirements. As a minimum, the
gas readings and fault status registers should be polled.
Description
Start
Address
End
Address
Size in
words
Access
ModBUS Data Table
Start Base Address
1000 1000 1 Read/Write
Factory Configuration
Data
Base +1 Base +18 18 Read Only
User Configuration
Data
Base +101 Base +148 48 Read/Write
Status Information
Base +201 Base +253 53 Read Only
Control Words
Base +301 Base +302 2 Read/Write
4.6. ModBUS Base Address (Read/Write)
The ModBUS base address register is located at address 1000 and has a default
value of 40000. This may be changed by writing a new value within the permis-
sible range to that address. Subsequent addresses must take this new base
address into consideration. The base address may be changed by writing to
address 1000, regardless of its contents.
Description Address Possible Value
ModBUS Data Table Base Address
1000 1000 - 60000
(default 40000)
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