73
Difference between I/O Refreshing in Customizable
Section 4-5
Exchanging Data between a Customizable Counter Unit and the CPU Unit
A CS1W-H
@@@@
Customizable Counter Unit exchanges data with the CS-
series CPU Unit in an asynchronous system using I/O refreshing timing on
both sides. (See Figure 1.)
Figure 1
• The Customizable Counter Unit refreshes its own I/O by reading the
shared memory inside it.
• The CPU Unit, on the other hand, refreshes its own I/O by reading the
shared memory in the Customizable Counter Unit.
This allows the Customizable Counter Unit and the CPU Unit to exchange
data (I/O refreshing). The CPU Unit, however, always has priority in accessing
the shared memory in the Customizable Counter Unit.
If the I/O refresh timing in the Customizable Counter Unit and the CPU Unit
synchronizes by chance, then the Customizable Counter Unit will not refresh
its data because the CPU Unit has priority in accessing the shared memory.
This means that the Customizable Counter Unit may not be refreshed for sev-
eral cycles.
Problem
The following problem may occur.
■
When the Same Constant Cycle Time Is Set for Both the CPU Unit and the
Customizable Counter Unit
When the constant cycle time function is used to set the same cycle time
interval for the CPU Unit and the Customizable Counter Unit, the I/O refresh
rate for both will overlap in consecutive cycles if the cycles ever become syn-
chronized. This means that the Customizable Counter Unit may not refresh
the I/O for several cycles. (See Figure 2.)
Figure 2
Cycle Time
CPU Unit
Asynchronous refresh
The CPU Unit has
priority in accessing
shared memory.
Customicable Counter Unit
Cycle time
Common processing
Status processing
Program execution
I/O refresh
Peripheral service
Shared
memory
Common processing
Status processing
Program execution
I/O refresh
Peripheral service
1 cycle
1 cycle
I/O refresh
CPU Unit
Customizable
Counter Unit
Summary of Contents for CS1W-HCA12-V1
Page 2: ......
Page 6: ...vi...
Page 20: ...xx Conformance to EC Directives 7...
Page 38: ...18 Models and System Configurations Section 1 2...
Page 78: ...58 Fail safe Circuits Section 3 5...
Page 138: ...118 AR Area Section 6 4...
Page 204: ...184 Improved Instructions Section 7 14...
Page 222: ...202 Cycle Time Section 8 3...
Page 240: ...220 Troubleshooting Flowcharts Section 9 5...
Page 244: ...224 Precautions when Using the CX Programmer Appendix A...
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