Renesas RL78/G1P Hardware User Manual page 714

16-bit single-chip microcontroller

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25.3 BCD Correction Circuit Operation

The basic operation of the BCD correction circuit is as follows.

(1) Addition: Calculating the result of adding a BCD code value and another BCD code value by using a BCD

<1> The BCD code value to which addition is performed is stored in the A register.

<2> By adding the value of the A register and the second operand (value of one more BCD code to be added) as

are in binary, the binary operation result is stored in the A register and the correction value is stored in the

BCD correction result register (BCDADJ).

<3> Decimal correction is performed by adding in binary the value of the A register (addition result in binary) and

the BCDADJ register (correction value), and the correction result is stored in the A register and CY flag.

Caution The value read from the BCDADJ register varies depending on the value of the A register

when it is read and those of the CY and AC flags. Therefore, execute the instruction <3>

after the instruction <2> instead of executing any other instructions. To perform BCD

correction in the interrupt enabled state, saving and restoring the A register is required

within the interrupt function. PSW (CY flag and AC flag) is restored by the RETI instruction.

An example is shown below.

Examples 1: 99 + 89 = 188

ADD A, !BCDADJ

Examples 2: 85 + 15 = 100

ADD A, !BCDADJ

Examples 3: 80 + 80 = 160

ADD A, !BCDADJ

R01UH0895EJ0100 Rev.1.00

Nov 29, 2019

CHAPTER 25 BCD CORRECTION CIRCUIT