7220 datasheet(37/303 Pages) RENESAS

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2-10

FUNCTIONAL DESCRIPTION

2.2 Access area

7220 Group User’s Manual

2.2.1 Zero page (addresses 000016 to 00FF16)

The 256 bytes from address 000016 to address 00FF16

are called “zero page”.

The internal RAM, I/O ports, timer, serial I/O, A-D

comparison, PWM output, CRT display and interrupt

related registers all present within this area.

These registers were called “special function registers”

in distinction from the accumulator, index registers

and so on in the CPU.

The addressing modes as shown in Table 2.2.1 are

used to specify memory (RAM) and special function

registers in the zero page area.

Those modes dedicated to the zero page area are

marked with a symbol (V).

This area can be accessed with shorter instructions

by using these modes.

Table 2.2.1 Zero page addressing

V Zero page

V Zero page Indirect

V Zero page X

V Zero page Y

V Zero page Bit

V Zero page Bit Relative

Absolute

Absolute X

Absolute Y

Relative

Indirect

Indirect X

Indirect Y

Bytes required

Addressing mode

2.2.2 Special page (addresses FF0016 to FFFF16)

The 256 bytes from address FF0016 to address FFFF16

within the internal ROM are called “special page

area”.

The addressing modes as shown in Table 2.2.2 are

used to specify memory in the special page area.

Those modes dedicated to the special page area

are marked with a symbol (V).

This area can be accessed with shorter instructions

by using these modes.

Subroutines used with considerable frequency are

ordinary assigned in this area.

Bytes required

Table 2.2.2 Special page addressing

Addressing mode

V Special page

Absolute

Absolute X

Absolute Y

Relative

Indirect

Indirect X

Indirect Y

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