External I/O Numbers - Hitachi HIDIC MICRO-EH Applications Manual

Chapter 6 I/O Specifications
6.2

External I/O Numbers

When starting an operation of the MICRO-EH, a user program is executed (scanned) after the input refresh processing
(receiving external input data) is performed. Operations are performed according to the contents of the user program, and
the next input refresh processing and output refresh processing (operation results are reflected in the external output) are
performed. After that, the next user program is executed (scanned). This series of operations is continually repeated until
the operation is stopped or until a problem occurs in which the operation can no longer continue.
When the operation is stopped or if a problem interrupting the operation occurs, the CPU performs output refresh
processing making all output data as off data and then stops the operation, regardless of the execution status of the user
program.
Figure 6.1 shows a diagram outlining this series of operations.
Input refresh processing Input refresh processing Output refresh processing
Time
RUN start
Execute (scan) user program System processing
Output refresh processing (off data)
Time
RUN stop
Execute (scan) user program
Figure 6.1 Overview of user program execution and refresh processing
The user programs are executed in sequence, normally beginning with the program in the beginning of the scan area till
the last program, or until the END instruction. Then, I/O data is refreshed prior to the execution of the next user program.
As shown above, external I/O data is updated in batch mode in the refresh processing after the user program is executed.
If it is necessary to update (refresh) the I/O data while the user program is being executed, use the refresh instruction.
When designing a system, take into account the above refresh operation from when the input data is received and
operated until output data is obtained.
6-3