Renesas H8/3847R Series Hardware Manual page 127

[B: BCLR instruction executed]
BSET #0 ,
[C: After executing BCLR]
P3
7
Input/output Output
Pin state Low
level
PCR3 1
PDR3 1
[D: Explanation of how BCLR operates]
When the BCLR instruction is executed, first the CPU reads PCR3. Since PCR3 is a write-only
register, the CPU reads a value of H'FF, even though the PCR3 value is actually H'3F.
Next, the CPU clears bit 0 in the read data to 0, changing the data to H'FE. Finally, this value
(H'FE) is written to PCR3 and BCLR instruction execution ends.
As a result of this operation, bit 0 in PCR3 becomes 0, making P3
and 6 in PCR3 change to 1, so that P3
To avoid this problem, store a copy of the PCR3 data in a work area in memory. Perform the bit
manipulation on the data in the work area, then write this data to PCR3.
[A: Prior to executing BCLR]
MOV. B #H'3F ,
MOV. B R0L ,
MOV. B R0L ,
P3
7
Input/output Input
Pin state Low
level
PCR3 0
PDR3 1
RAM0 0
The BCLR instruction is executed designating PCR3.
@PCR3
P3 P3
6 5
Output Output
High Low
level level
1 1
0 0
and P3
7
The PCR3 value (H'3F) is written to a work area in
R0L
memory (RAM0) as well as to PCR3.
@RAM0
@PCR3
P3 P3
6 5
Input Output
High Low
level level
0 1
0 0
0 1
P3 P3
4 3
Output Output
Low Low
level level
1 1
0 0
an input port. However, bits 7
0
change from input pins to output pins.
6
P3 P3
4 3
Output Output
Low Low
level level
1 1
0 0
1 1
Rev. 6.00 Aug 04, 2006 page 89 of 680
Section 2 CPU
P3 P3 P3
2 1
Output Output Input
Low Low High
level level level
1 1 0
0 0 0
P3 P3 P3
2 1
Output Output Output
Low Low Low
level level level
1 1 1
0 0 0
1 1 1
REJ09B0145-0600
0
0