7643 datasheet(8/121 Pages) RENESAS

8 / 121 page

7643 Group

Rev.2.00

Aug 28, 2006

page 8 of 119

REJ03B0054-0200

FUNCTIONAL DESCRIPTION

CENTRAL PROCESSING UNIT (CPU)

The 7643 group uses the standard 7600 series instruction set. Refer

to the 7600 Series Software Manual for details on the instruction set.

The 7600 series has an upward compatible instruction set, of which

instruction execution cycles are shortened, for 740 series.

[Accumulator (A)]

The accumulator is an 8-bit register. Data operations such as data

transfer, etc., are executed mainly through the accumulator.

[Index Register X (X)]

The index register X is an 8-bit register. In the index addressing modes,

the value of the OPERAND is added to the contents of register X and

specifies the real address.

[Index Register Y (Y)]

The index register Y is an 8-bit register. In partial instruction, the

value of the OPERAND is added to the contents of register Y and

specifies the real address.

[Stack Pointer (S)]

The stack pointer is an 8-bit register used during subroutine calls

and interrupts. This register indicates start address of stored area

(stack) for storing registers during subroutine calls and interrupts.

The low-order 8 bits of the stack address are determined by the con-

tents of the stack pointer. The high-order 8 bits of the stack address

are determined by the stack page selection bit. If the stack page

selection bit is “0” , the high-order 8 bits becomes “0016”. If the stack

page selection bit is “1”, the high-order 8 bits becomes “0116”.

The operations of pushing register contents onto the stack and pop-

ping them from the stack are shown in Figure 7.

Store registers other than those described in Figure 7 with program

when the user needs them during interrupts or subroutine calls.

[Program Counter (PC)]

The program counter is a 16-bit counter consisting of two 8-bit regis-

ters PCH and PCL. It is used to indicate the address of the next in-

struction to be executed.

Fig. 6 7600 series CPU register structure

Accumulator

b15

Index register X

Index register Y

Stack pointer

PCL

Program counter

PCH

N V T B D I Z C

Processor status register (PS)

Carry flag

Zero flag

Interrupt disable flag

Decimal mode flag

Break flag

Index X mode flag

Overflow flag

Negative flag

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