Rockwell Automation 1747-DSN DISTRIBUTED I/O SCANNER - Manual (Page 22)

Chapter 3
Configuration and Programming
3–4
7 I/O Block Configuration Output Image
The 7 I/O block Configuration Output Image consists of eight words (one
control word and seven output words). Each output word corresponds to an
I/O block address. For example, the output data for I/O block 7 is located in
output word 7. In addition, the bits of each output word correspond to the
outputs on the I/O block. For example,
•
For I/O blocks with 6 outputs, bits 0 – 5 are valid.
•
For I/O blocks with 8 outputs, bits 0 – 7 are valid.
Control Word (Word 0)
The control word controls the following three functions:
Number of I/O Blocks – bits 0 – 4 configure the scanner for the number of
I/O blocks physically connected to the scanner. I/O blocks must be
numbered consecutively, starting with one. They do not have to be wired in
a contiguous order.
•
The maximum number of I/O blocks you can configure is 7. Any number
larger than 7 causes configuration error
xx62 in SLC 5/02 and xx58 in
SLC 5/01.
•
When bits 0 – 4 equal 0, the system defaults to 7, the maximum number
of I/O blocks allowed for this configuration.
•
Configure the scanner for the number of I/O blocks connected. If you
configure it for more I/O blocks than what you have connected, you will
waste throughput time trying to scan I/O blocks that do not exist on the
link. If you configure it for fewer I/O blocks than you have connected,
the scanner will not communicate with I/O blocks which have higher
address numbers than the number of configured I/O blocks.
Disable Outputs – When bit 9 is set and the SLC processor is in run mode,
the scanner disables all outputs on all I/O blocks. Whether the disabled
outputs are reset to 0 or held in their last state depends on the Hold Last State
dip switch setting (located on each I/O block).
•
If bit 9 is set and the Hold Last State function is disabled, the outputs will
be reset to 0.
•
If bit 9 is set and the Hold Last State function is enabled, the outputs are
held in their last state.
Important: The Disable Outputs bit is constantly monitored by the scanner
when the SLC processor is in run mode.