Example 2: BSET instruction executed designating port 3
P37 and P36 are designated as input pins, with a low-level signal input at P37 and a high-level
signal at P36. The remaining pins, P35 to P30, are output pins and output low-level signals. In this
example, the BSET instruction is used to change pin P30 to high-level output.
[A: Prior to executing BSET]
P37
P36
P35
P34
P33
P32
P31
P30
Input/output
Pin state
Input
Input
Output Output
Output
Output
Output
Output
Low
level
High
level
Low
Low
Low
level
Low
level
Low
level
Low
level
level
level
PCR3
PDR3
0
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
[B: BSET instruction executed]
BSET #0 @PDR3
,
The BSET instruction is executed designating port 3.
[C: After executing BSET]
P37
P36
P35
P34
P33
P32
P31
P30
Input/output
Pin state
Input
Input
Output
Output
Output
Output
Output
Output
Low
level
High
level
Low
level
Low
level
Low
level
Low
level
Low
level
High
level
PCR3
PDR3
0
0
0
1
1
0
1
0
1
0
1
0
1
0
1
1
[D: Explanation of how BSET operates]
When the BSET instruction is executed, first the CPU reads port 3.
Since P37 and P36 are input pins, the CPU reads the pin states (low-level and high-level input).
P35 to P30 are output pins, so the CPU reads the value in PDR3. In this example PDR3 has a value
of H'80, but the value read by the CPU is H'40.
Next, the CPU sets bit 0 of the read data to 1, changing the PDR3 data to H'41. Finally, the CPU
writes this value (H'41) to PDR3, completing execution of BSET.
As a result of this operation, bit 0 in PDR3 becomes 1, and P30 outputs a high-level signal.
However, bits 7 and 6 of PDR3 end up with different values.
58
ETC [ ETC ]
