Data Exchange
The Input Data Input data and I/O status information from the I/O modules are sent to the input
and I/O Status process image area. The fieldbus master or another monitoring device, e.g., an HMI
Process Image panel (See The HMI Blocks in the Island Data Image, p. 170), can view data in the input data image area.
All eight I/O modules are represented in the input process image area. Their assigned registers start at register 45392 and continue in the order of their island bus addresses.
A digital I/O module uses two contiguous registers:
Digital input modules use one register to report data and the next to report status. Digital output modules use one register to report echo output data and the next to report status.
Note: The value in an echo output data register is basically a copy of the value written to the corresponding register in the output data process image area (See The Output Data Process Image, p. 119). Generally, the fieldbus master writes this value to the NIM, and the echo is of not much interest. If an output channel is configured to perform a reflex action (See What Is a Reflex Action?, p. 156), however, the echo register provides a location where the fieldbus master can view the current value of the output.
The analog input module uses four contiguous registers: the first register to report the data for channel 1
the second register to report status for channel 1 the third register to report the data for channel 2 the fourth register to report status for channel 2
The analog output module uses two contiguous registers:
the first register to report status for channel 1 the second register to report status for channel 2
120 | 890USE17700 April 2004 |
