Writing Outputs to Specialty I/O
During this portion of the cycle the CPU writes any output points associated with the
following.
• Remote I/O
• Specialty Modules (such as High-Speed Counter, etc.)
The time required to write any output image register data to these modules depends on which
CPU you are using, the number of modules, and the number of output points.
For example, the time required for a DL240 to write two 8-point output modules (located in
a Remote base) would be calculated as follows, where NM is the number of modules and NO
is the total number of output points:
Remote I/O
Formula
Time = 6 µs + (67.5 µs x NM) + (46 µs x NO)
Example
Time = 6 µs + (67.5 µs x 2) + (46 µs x 16)
Time = 877 µs
NOTE: This total time is the actual time required for the CPU to update these outputs. This does not include
any additional time that is required for the CPU to actually service the particular specialty modules.
Diagnostics
The DL205 CPUs perform many types of system diagnostics. The amount of time required
depends on many things, such as the number of I/O modules installed, etc. The following
table shows the minimum and maximum times that can be expected.
DL205 User Manual, 4th Edition, Rev. B
3–33
Chapter 3: CPU Specifications and Operations
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A
B
C
D
Remote Module DL230 DL240 DL250–1 DL260
Overhead
N/A 6.0 µs 1.9 µs 1.9 µs
Per module (with outputs)
N/A 67.5 µs 17.7 µs 17.7 µs
Per output point
N/A 46.0 µs 3.2 µs 3.2 µs
Diagnostic Time DL230 DL240 DL250–1 DL260
Minimum
600.0 µs 422.0 µs 26.8 µs 26.8 µs
Maximum
900.0 µs 855.0 µs 103.0 µs 103.0 µs
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