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7470/7471/7477/7478 GROUP USER’S MANUAL

HARDWARE

1.8 Access area

1-29

1.8.1 Zero page (Addresses 000016 to 00FF16)

The area of 256 bytes from addresses 000016 to 00FF16 is called the zero page. The internal RAM and

the special function register (SFR) are located in this area.

To specify a memory or a register in this area, use the addressing mode shown in Table 1.8.1. In this

area, especially, it is possible to access this area in a shorter instruction cycle by using the zero addressing

mode.

1.8.2 Special page (Addresses FF0016 to FFFF16)

The area of 256 bytes from addresses FF0016 to FFFF16 is called the special page. The internal ROM

and the interrupt vector area are located in this area.

To specify a memory or subroutine in this area, use the addressing mode shown in Table 1.8.1. In this

area, especially, it is possible to jump to this area in a shorter instruction cycle by using the special page

addressing mode.

Ordinary, subroutines with high frequency of use are located in this area.

Table 1.8.1 Addressing mode accessible to each area

Addressing mode (bytes required)

Zero page (2)

Zero page indirect (2)

Zero page X (2)

Zero page Y (2)

Zero page bit (2)

Zero page bit relative (3)

Absolute (3)

Absolute X (3)

Absolute Y (3)

Relative (2)

Indirect (3)

Indirect X (2)

Indirect Y (2)

Special page (2)

Special page reference

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Other area reference

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Zero page reference

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