鈥?/div>
Description on operation
1. When the BCLR instruction is executed, first the CPU reads PCR5. Since PCR5 is a write-only
register, the CPU reads a value of H'FF, even though the PCR5 value is actually H'3F.
2. Next, the CPU clears bit 0 in the read data to 0, changing the data to H'FE.
3. Finally, H'FE is written to PCR5 and BCLR instruction execution ends.
As a result of this operation, bit 0 in PCR5 becomes 0, making P50 an input port. However,
bits 7 and 6 in PCR5 change to 1, so that P57 and P56 change from input pins to output pins.
To prevent this problem, store a copy of the PDR5 data in a work area in memory and
manipulate data of the bit in the work area, then write this data to PDR5.
Rev. 4.00, 03/04, page 45 of 400