H83834U Datasheet, PDF (72/497 Pages) Renesas Technology Corp – Single-Chip Microcomputer

[C: After executing BCLR]
Input/output
Pin state
PCR3
PDR3
P3₇
Output
Low
level
1
1
P3₆
Output
High
level
1
0
P3₅
Output
Low
level
1
0
P3₄
Output
Low
level
1
0
P3₃
Output
Low
level
1
0
P3₂
Output
Low
level
1
0
P3₁
Output
Low
level
1
0
P3₀
Input
High
level
0
0
[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 P3₀ an input port. However, bits 7
and 6 in PCR3 change to 1, so that P3₇ and P3₆ 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 #3F, R0L
MOV. B R0L, @RAM0
MOV. B R0L, @PCR3
The PCR3 value (H'3F) is written to a work area in memory
(RAM0) as well as to PCR3.
Input/output
Pin state
PCR3
PDR3
RAM0
P3₇
Input
Low
level
0
1
0
P3₆
Input
High
level
0
0
0
P3₅
Output
Low
level
1
0
1
P3₄
Output
Low
level
1
0
1
P3₃
Output
Low
level
1
0
1
P3₂
Output
Low
level
1
0
1
P3₁
Output
Low
level
1
0
1
P3₀
Output
Low
level
1
0
1
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