Rockwell Automation 1746-FIO4V SLC 500 Fast Analog I/O/ User Manual - Manual (Page 30)

Publication 1746-UM009B-EN-P - September 2007
30 Processor and Module Considerations
Processor Considerations Knowing how the processor works helps you program it more
effectively.
Processor Update of Analog I/O Data
Analog input and output image words are updated by the processor
once every processor scan when the processor scans data and
program files in succession.
Processor scan time depends largely on the size of your program files:
the greater the number of programming instructions, the longer the
time to scan the file. Some instructions take longer to scan than
others.
For information on processor scan time and instruction execution
time, refer to the SLC 500 Instruction Set Reference Manual,
publication 1747-RM001.
If an application requires processor updates of analog data more
frequently than once per scan, use Immediate Input or Immediate
Output instructions. These instructions typically update an analog
channel in 1 ms, but also increase the overall scan time by the same
amount.
Typical update times for SLC processors are:
• 10 ms for a typical 1K program.
• 1 ms per analog channel when using immediate I/O instructions.
Monitor Analog I/O Data
You can monitor analog input and output data in binary or decimal
format. You select the format by its radix. The default radix is binary.
Binary data is presented in 2’s-complement format. Changing the radix
to decimal lets you view analog I/O data as decimal representations of
integer words.
Refer to 2’s-complement Binary Numbers on page 83 for more
information.
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