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Chapter 5 CPU Registers
2.Dedicated Registers
2.7 MDH, MDL: Multiply & Divide Register
Multiply & Divide register (MDH/MDL) consists of 32 bits.
Figure 2-12 Bit Structure of Multiply & Divide Register (MDH/MDL)
This is the register for multiplication and division and consists of 32 bits.
Initial value by reset is indeterminate.
■ At the executing multiplication
When 32 bits x 32 bits multiplication, operation results of 64 bits are stored in multiplication/division store register as
the following allocation.
• MDH: Upper 32 bits
• MDL: Lower 32 bits
When 16 bits x 16 bits multiplication, results are stored as follows.
• MDH: Indeterminate.
• MDL: Results of 32 bits
■ At the executing division
Upon starting operation, dividend is stored in MDL.
By computing division by executing DIV0S/DIV0U, DIV1, DIV2, DIV3, or DIV4S instruction, results are stored in MDL
and MDH.
• MDH: Remainder
• MDL: Quotient
31 0
MDH
MDL