UPD17P136ACT datasheet(118/292 Pages) NEC

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CHAPTER 11 ARITHMETIC AND LOGIC UNIT (ALU)

11.7 ROTATIONS

There are rotation instructions for rotation to the right and for rotation to the left.

The RORC instruction is used for rotation to the right.

The RORC instruction can only be used with the general register.

Rotation using the RORC instruction is not affected by the BCD or CMP flags in the program status word (PSWORD)

and does not affect the Z flag in the program status word (PSWORD).

Rotation to the left is performed by using the addition instruction ADDC.

11.7.1 and 11.7.2 explain rotation.

11.7.1 Rotation to the Right

The instruction used for rotation to the right (RORC r) rotates the contents of the general register in the direction

of its least significant bit.

When this instruction is executed, the contents of the CY flag becomes the most significant bit of the general register

(bit 3) and the least significant bit of the general register is placed in the CY flag.

Example 1.

MOV

PSW,

#0100B

; Sets CY flag to 1.

MOV

R1,

#1001B

RORC

When these instructions are executed, the following operation is performed.

Basically, when rotation to the right is performed, the following operation is executed:

CY flag

→ b3, b3 → b2, b2 → b1, b1 → b0, b∞ → CY flag.

MOV

PSW,

#0000B

; Resets CY flag to 0.

MOV

R1,

#1000B

; MSB

MOV

R2,

#0100B

MOV

R3,

#0010B

; LSB

RORC

The program code above rotates the 13 bits in R1, R2, and R3 to the right.

CY flag

UPD17P136ACT Datasheet(PDF) 118 Page - NEC

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