Automationdirect.com DirectLOGIC DL205 Series User Manual page 123

Chapter 3: CPU Specifications and Operations
During the Service Peripherals portion of the scan, the CPU analyzes the communications
request and responds as appropriate. The amount of time required to service the peripherals
1
depends on the content of the request.
2 To Service Request
Minimum
Run Mode Max.
3
Program Mode Max.
4
CPU Bus Communication
Some specialty modules can also communicate directly with the CPU via the CPU bus.
During this portion of the cycle the CPU completes any CPU bus communications. The
5
actual time required depends on the type of modules installed and the type of request being
processed.
6
NOTE: Some specialty modules can have a considerable impact on the CPU scan time. If timing is critical
in your application, consult the module documentation for any information concerning the impact on the
7
scan time.
8
Update Clock/Calendar, Special Relays, Special Registers
The clock, calendar, and special relays are updated and loaded into special V-memory
locations during this time. This update is performed during both Run and Program Modes.
9
Modes
10
Program Mode
11
Run Mode
12
Writing Outputs
The time required to write the output status for the local and expansion I/O modules
13
depends on which CPU you are using and the number of output points in the base. The
following table shows typical update times required by the CPU.
14
Timing Factors
Overhead
A
Per output point
For example, the time required for a DL240 to write data for two 8-point output modules
B
would be calculated as follows (where NO is the total number of output points):
Formula
C
Time = 33 + (NO x 14.6µs)
Example
D
Time = 33 + (16 x 14.6µs)
Time = 266.6µs
3–32
DL205 User Manual, 4th Edition, Rev. B
DL230
260 µs
30 ms
3.5 Seconds
DL230
Minimum 8.0 µs fixed
Maximum 8.0 µs fixed
Minimum 20.0 µs
Maximum 26.0 µs
DL230
66.0 µs
8.5 µs
DL240
250 µs 8 µs
20 ms 410 µs
4 Seconds 2 Seconds
DL240
35.0 µs
48.0 µs
60.0 µs
85.0 µs
DL240
33.0 µs 28.1 µs
14.6 µs 3.0 µs
DL250–1 DL260
8 µs
410 µs
3.7 Seconds
DL250–1
11.0 µs 11.0 µs
11.0 µs 11.0 µs
19.0 µs 19.0 µs
26.0 µs 26.0 µs
DL250–1 DL260
28.1 µs
3.0 µs
DL260