Datasheet

Section 2 CPU
Rev. 6.00 Aug 04, 2006 page 89 of 680
REJ09B0145-0600
[B: BCLR instruction executed]
BSET #0 , @PCR3 The BCLR instruction is executed designating PCR3.
[C: After executing BCLR]
P3
7
P3
6
P3
5
P3
4
P3
3
P3
2
P3
1
P3
0
Input/output Output Output Output Output Output Output Output Input
Pin state Low
level
High
level
Low
level
Low
level
Low
level
Low
level
Low
level
High
level
PCR3 11111110
PDR3 10000000
[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
0
an input port. However, bits 7
and 6 in PCR3 change to 1, so that P3
7
and P3
6
change from input pins to output pins.
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
MOV. B
MOV. B
#H'3F
R0L
R0L
,
,
,
R0L
@RAM0
@PCR3
The PCR3 value (H'3F) is written to a work area in
memory (RAM0) as well as to PCR3.
P3
7
P3
6
P3
5
P3
4
P3
3
P3
2
P3
1
P3
0
Input/output Input Input Output Output Output Output Output Output
Pin state Low
level
High
level
Low
level
Low
level
Low
level
Low
level
Low
level
Low
level
PCR3 00111111
PDR3 10000000
RAM0 00111111