Filter
Top Products
Advanced Configuration Features
890USE17700 April 2004 165
A Modbus View of the Island’s Data Image
Summary A block of Modbus registers is reserved in the NIM to hold and maintain the island’s
data image. Overall, the data image holds 9999 registers. The registers are divided
into nine contiguous groups (or blocks), each dedicated to a specific purpose.
Modbus
Registers and
Their Bit
Structure
Registers are16-bit constructs. The most significant bit (MSB) is bit 15, which is
displayed as the leftmost bit in the register. The least significant bit (LSB) is bit 0,
displayed as the rightmost bit in the register:
The bits can be used to display operating data or device/system status.
Each register has a unique reference number, starting at 40001. The content of each
register, represented by its 0/1 bit pattern, may be dynamic, but the register
reference and its assignment in the control logic program remain constant.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
MSB LSB