Specifications

Advanced Configuration Features

110

31004624 8/2009

The Island’s Process Image Blocks

Summary

Two blocks of registers in the island’s data image (see page 108) are the focus for

this discussion. The first block is the output data process image, which starts at

status process image, which also consumes 4096 registers (45392 through 49487).

The registers in each block are used to report island bus device status and to

dynamically exchange input or output data between the fieldbus master and the

island’s I/O modules.

Output Data Process Image

The output data block (registers 40001 through 44096) handles the output data

process image. This process image is a Modbus representation of the control data

that has just been written from the fieldbus master to the NIM. Only data for the

island’s output modules is written to this block.

Output data is organized in 16-bit register format. One or more registers are

dedicated to the data for each output module on the island bus.

For example, say you are using a two-channel digital output module as the first

output module on your island bus. Output 1 is on and output 2 is off. This information

would be reported in the first register in the output data process image, and it would

look like this:

where:

z Normally, a value of 1 in bit 0 indicates that output 1 is on.

z Normally, a value of 0 in bit 1 indicates that output 2 is off.

z The remaining bits in the register are not used.

Some output modules, such as the one in the example above, utilize a single data

example, would use separate registers to represent the values for each channel,

and might use the 11 or 12 most significant bits to display analog values in

IEC format.

Registers are allocated to output modules in the output data block according to their

addresses on the island bus. Register 40001 always contains the data for the first

output module on the island (the output module closest to the NIM).