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Example 2: Here a BSET instruction is executed designating port 6.
P6
7
and P6
6
are designated as input pins, with a low-level signal input at P6
7
and a high-level
signal at P6
6
. The remaining pins, P6
5
to P6
0
, are output pins and output low-level signals. In this
example, the BSET instruction is used to change pin P6
0
to high-level output.
[A: Prior to executing BSET]
P6
7
P6
6
P6
5
P6
4
P6
3
P6
2
P6
1
P6
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
PCR6
0
0
1
1
1
1
1
1
PDR6
1
0
0
0
0
0
0
0
[B: BSET instruction executed]
BSET #0, @PDR6
The BSET instruction is executed designating port 6.
[C: After executing BSET]
P6
7
P6
6
P6
5
P6
4
P6
3
P6
2
P6
1
P6
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
High
level
PCR6
0
0
1
1
1
1
1
1
PDR6
0
1
0
0
0
0
0
1
[D: Explanation of how BSET operates]
When the BSET instruction is executed, first the CPU reads port 6.
Since P6
7
and P6
6
are input pins, the CPU reads the pin states (low-level and high-level input).
P6
5
to P6
0
are output pins, so the CPU reads the value in PDR6. In this example PDR6 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 PDR6 data to H'41. Finally, the CPU
writes this value (H'41) to PDR6, completing execution of BSET.
As a result of this operation, bit 0 in PDR6 becomes 1, and P6
0
outputs a high-level signal.
However, bits 7 and 6 of PDR6 end up with different values.
