7220 Datasheet, PDF (37/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.2 Access area
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
Addressing mode
V Zero page
V Zero page Indirect
V Zero page X
V Zero page Y
V Zero page Bit
V Zero page Bit Relative
Bytes required
2
2
2
2
2
3
Absolute
3
Absolute X
3
Absolute Y
3
Relative
2
Indirect
3
Indirect X
2
Indirect Y
2
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.
Table 2.2.2 Special page addressing
Addressing mode
Bytes required
V Special page
2
Absolute
3
Absolute X
3
Absolute Y
3
Relative
2
Indirect
3
Indirect X
2
Indirect Y
2
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7220 Group User’s Manual