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HD6433644R Datasheet(PDF) 75 Page - Renesas Technology Corp |
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HD6433644R Datasheet(HTML) 75 Page - Renesas Technology Corp |
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75 / 549 page ![]() Section 2 CPU Rev. 6.00 Sep 12, 2006 page 55 of 526 REJ09B0326-0600 Bit Manipulation in a Register Containing a Write-Only Bit Example 3: BCLR instruction executed designating port 3 control register PCR3 As in the examples above, P37 and P36 are 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 that output low-level signals. In this example, the BCLR instruction is used to change pin P30 to an input port. It is assumed that a high-level signal will be input to this input pin. [A: Prior to executing BCLR] P37 P36 P35 P34 P33 P32 P31 P30 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 0 0 1 1 1 1 1 1 PDR3 1 0 0 0 0 0 0 0 [B: BCLR instruction executed] BCLR #0 , @PCR3 The BCLR instruction is executed designating PCR3. [C: After executing BCLR] P37 P36 P35 P34 P33 P32 P31 P30 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 1 1 1 1 1 1 1 0 PDR3 1 0 0 0 0 0 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. |
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