![Hitachi H8/3008 Hardware Manual Download Page 56](http://html.mh-extra.com/html/hitachi/h8-3008/h8-3008_hardware-manual_140473056.webp)
40
Before Execution of BCLR Instruction
P4
7
P4
6
P4
5
P4
4
P4
3
P4
2
P4
1
P4
0
Input/output
Input
Input
Output
Output
Output
Output
Output
Output
DDR
0
0
1
1
1
1
1
1
Execution of BCLR Instruction
BCLR #0, P4DDR
;
Execute BCLR instruction on DDR
After Execution of BCLR Instruction
P4
7
P4
6
P4
5
P4
4
P4
3
P4
2
P4
1
P4
0
Input/output
Output
Output
Output
Output
Output
Output
Output
Input
DDR
1
1
1
1
1
1
1
0
Explanation: To execute the BCLR instruction, the CPU begins by reading P4DDR. Since
P4DDR is a write-only register, it is read as H'FF, even though its true value is H'3F.
Next the CPU clears bit 0 of the read data, changing the value to H'FE.
Finally, the CPU writes this value (H'FE) back to P4DDR to complete the BCLR instruction.
As a result, P4
0
DDR is cleared to 0, making P4
0
an input pin. In addition, P4
7
DDR and P4
6
DDR
are set to 1, making P4
7
and P4
6
output pins.
The BCLR instruction can be used to clear flags in the on-chip registers to 0. In the case of the
IRQ status register (ISR), for example, a flag must be read as a condition for clearing it, but when
using the BCLR instruction, if it is known that a flag has been set to 1 in an interrupt-handling
routine, for instance, it is not necessary to read the flag ahead of time.
Summary of Contents for H8/3008
Page 1: ...Hitachi 16 Bit Microcomputer H8 3008 Hardware Manual ADE 602 221 Rev 1 0 9 14 00 Hitachi Ltd ...
Page 4: ......
Page 17: ...xii ...
Page 70: ...54 ...
Page 114: ...98 ...
Page 154: ...138 ...
Page 314: ...298 ...
Page 412: ...396 ...
Page 496: ...480 ...