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FUNCTIONAL DESCRIPTION
2.2 Access area
2.2.1 Zero page (addresses 0000
The 256 bytes from address 0000
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 ( ).
This area can be accessed with shorter instructions
by using these modes.
2.2.2 Special page (addresses FF00
The 256 bytes from address FF00
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 ( ).
This area can be accessed with shorter instructions
by using these modes.
Subroutines used with considerable frequency are
ordinary assigned in this area.
2-10
to 00FF
)
16
16
to address 00FF
16
16
to FFFF
)
16
16
to address FFFF
16
16
7220 Group User's Manual
Table 2.2.1 Zero page addressing
Addressing mode
Zero page
Zero page Indirect
Zero page X
Zero page Y
Zero page Bit
Zero page Bit Relative
Absolute
Absolute X
Absolute Y
Relative
Indirect
Indirect X
Indirect Y
Table 2.2.2 Special page addressing
Addressing mode
Special page
Absolute
Absolute X
Absolute Y
Relative
Indirect
Indirect X
Indirect Y
Bytes required
2
2
2
2
2
3
3
3
3
2
3
2
2
Bytes required
2
3
3
3
2
3
2
2
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