Specifications

Fieldbus Communications Support
66
31004624 8/2009
Process Data Flow
During data exchange, the master writes the output image, including the control
word. The high byte of the master’s control word specifies the information requested
from slave devices. The slaves respond with a status word in which the high byte
(selector) value corresponds to that of the control word.
The correspondence of high byte values for the control and status words are shown
in the following figure:
1 output image control word (written by the master)
2 input image status word (transmitted by the NIM)
3 control word high byte (selector)
4 control word low byte (inconsequential value)
5 status word high byte (selector)
6 status word low byte (contains the information requested by the master)
The default control word value (0) will return NIM status and diagnostics information
in the low byte of the status word.