Hitachi H8/3672 Series Hardware Manual page 63

Prior to executing BCLR
P57
Input/output Input
Pin state Low
level
PCR5 0
PDR5 1
BCLR instruction executed
BCLR #0,
After executing BCLR
P57
Input/output Output
Pin state Low
level
PCR5 1
PDR5 1
Description on operation
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.
Next, the CPU clears bit 0 in the read data to 0, changing the data to H'FE.
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 PCR5 data in a work area in memory and manipulate data of the
bit in the work area, then write this data to PCR5.
P56 P55
Input Output
High Low
level level
0 1
0 0
The BCLR instruction is executed for PCR5.
@PCR5
P56 P55
Output Output
High Low
level level
1 1
0 0
P54 P53 P52
Output Output Output
Low Low Low
level level level
1 1 1
0 0 0
P54 P53 P52
Output Output Output
Low Low Low
level level level
1 1 1
0 0 0
Rev. 1.0, 03/01, page
P51 P50
Output Output
Low Low
level level
1 1
0 0
P51 P50
Output Input
Low High
level level
1 0
0 0
39 280
of