Rockwell Automation 1747-DSN DISTRIBUTED I/O SCANNER - Manual (Page 28)

Chapter 3
Configuration and Programming
3–10
The bits in the Communication Status Word(s) indicate whether or not the
scanner is communicating with each of the configured I/O blocks. Each bit
in the Communication Status Word(s) corresponds to an I/O block. If the
scanner is communicating with an I/O block, the corresponding bit in the
Communication Status Word is set to 1. The bits in the Communication
Status Word(s) can be used to:
•
ensure that the I/O block(s) are communicating with the scanner before
any input data from the I/O block(s) is used by the SLC processor
program.
•
have the SLC processor set an alarm or take appropriate action if
communication with an I/O block(s) is lost.
In addition to the Communication Status Bits for each individual I/O block,
the 30 I/O block Configuration has an Overall Communication Status Bit (bit
0 of word 0). This bit is set to 1 when all of the configured I/O blocks are
communicating with the scanner.
For example, if the scanner is configured for 4 I/O blocks, the Overall
Communication Status bit will be 1 when all four I/O blocks are
communicating. It will be set to 0 if any one of the I/O blocks is not
communicating. By monitoring this bit, the SLC processor can quickly
determine if communication with any configured I/O block has been lost.
The application example on page 3–11 illustrates a use of the
Communication Status Word.
The Control Word operates the same in both the 7 and 30 I/O block
Configurations. It is used to:
•
configure the scanner for the exact number of I/O blocks that are on the
DIO Link (Number of I/O blocks, bits 0–4),
•
start the scanner communicating with the I/O Blocks (Configuration Data
Valid Bit, bit 10)
•
disable the I/O block outputs (Disable Output Bit, bit 9).
To start the scanner communicating with the I/O blocks when the SLC
processor enters run mode, the SLC processor program should:
•
load the correct Number of I/O Blocks to bits 0 to 4
•
set the Configuration Data Valid bit
Any further transitions of bits 0–4 (Number of I/O Blocks) while the SLC
processor is in run mode are ignored. Do not reset the Configuration Data
Valid bit to 0 during program execution. To change the number of I/O blocks
to which the scanner is communicating, the SLC processor must be taken out
of run mode.
Use of the Communication
Status Words
Use of the Control Word