Fujitsu FR81 3.3.12 Multiplication/Division Register (MDH, MDL)

FR81 Family

30 FUJITSU MICROELECTRONICS LIMITED CM71-00105-1E

CHAPTER 3 PROGRAMMING MODEL

3.3

The reset value of table base register (TBR) is 000F FC00H. Do not set a value above FFFF FC00H for the

table base register (TBR).

Precautions:

If values greater than FFFF FC00H are assigned to the table base register (TBR), this operation may

result in an overflow when summed with the offset value. An overflow in turn will result in vector

access to the area 0000 0000H to 0000 03FFH, which can cause a program run away.

3.3.12 Multiplication/Division Register (MDH, MDL)

Multiplication/Division register (MDH, MDL) is a 64-bit register comprised of MDH represented by the

higher 32 bits and MDL represented by the lower 32 bits. During multiplication, the product is stored.

During division, the value set for the dividend and the quotient is stored.

Figure 3.3-18 shows the bit configuration of Multiplication/Division register (MDH, MDL).

Figure 3.3-18 Multiplication/Division Register (MDH, MDL) Bit Configuration

The function of Multiplication/Division register (MDH, MDL) is different during a multiplication and

during a division operation.

●Function during Multiplication

In case of a 32 bit × 32 bit multiplication (MUL, MULU instruction), the calculation result of 64-bit length

is stored in the product register (MDH, MDL) as follows.

MDH: higher 32 bits

MDL: lower 32 bits

In case of a 16 bit × 16 bit multiplication (MULH, MULUH instruction), the calculation result of 32-bit

length is stored in the product register (MDH, MDL) as follows.

MDH: undefined

MDL: result 32 bits

Figure 3.3-19 shows an example of multiplication operation using Multiplication/Division register (MDH,

MDL).

MDH

MDL

bit31bit0 Initial value

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