FUJITSU MB91F109 FR30 - Manual (Page 321)

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13.3 Bit Search Module Operation and Save/Restore Processing
■ Save/Restore Processing
When the internal status of the bit search module must be saved and restored, such as when the
module is used in the interrupt handler, proceed as follows:
1. Read the 1-detection data register and store the read data. (Save)
2. Use the bit search module.
3. Write the data saved in step 1) to the 1-detection data register. (Restore)
As a result of the above operation, the value obtained by reading the next detection result register
corresponds to the data written to the bit search module before step 1).
Even if the last register to which data was written is a 0-detection or point-change detection
register, the data can be restored by proceeding as above.