HT9580 datasheet(46/63 Pages) HOLTEK

46 / 63 page

HT9580

April 28, 2000

Preliminary

Addressing modes

The M6502 supports fifteen (15) addressing

modes, shown in table below. In interpreting

this table you should note that:

· The byte following a 2 byte opcode = IAL (typ.)

· The 2 bytes following a 3 byte opcode = BAL

and BAH (typ.)

· Standard assembly notation is used

· A number in parenthesis indicates that the

contents of the location pointed to by the

number are to be used. For example (12H) in-

dicates the contents of address 12H.

· A comma in the address is used to indicate the

high and low byte of an address. For example

(01H, AAH) indicates the contents of address

01AAH.

Mode

Description

IMP

IMPLIED: The data is implied in the opcode (example: CLC)

ACC

ACCUMULATOR: The accumulator is used as the source data. (data=AREG)

IMM

IMMEDIATE: The byte following the opcode is the data. (data=IAL)

ZPG

ZERO PAGE: The first 256 RAM locations (0000H~00FFH) are used for fast access

and small code size. The upper 8-bit of the address are always zero. [data=(00, IAL)]

ZPX

ZERO PAGE INDIRECT X: The X register is added to the byte following the opcode to

give a new zero page address. Note that the upper 8-bit of the address are always zero.

[data=(00, IAL+X)]

ZPY

ZERO PAGE INDIRECT Y: The Y register is added to the byte following the opcode to

give a new zero page address. Note that the upper 8-bit of the address are always zero.

Only the LDX and the STX opcodes use this mode. [data=(00, IAL+Y)]

ABS

ABSOLUTE: The two bytes following the opcode give the absolute address of the data.

[data=(BAH, BAL)]

ABX

ABSOLUTE X: The X register is added to the two bytes following the opcode to produce

a new 16-bit address. {data=[(BAH, BAL)]+X}

ABY

ABSOLUTE Y: The Y register is added to the two bytes following the opcode to produce

a new 16-bit address. {data=[(BAH, BAL)]+Y}

ABI

ABSOLUTE INDIRECT: The two bytes following the opcode are used as a pointer to

memory. Only the JMP opcode uses this mode. [data=(BAH, BAL)]

AIX

INDEXED ABSOLUTE INDIRECT X: The two bytes following the opcode are added to

the X register to yield a new 16-bit address. The contents of this address and the fol-

lowing one are used as an indirect address. Only the JMP opcode uses this mode.

{data=[(BAH, BAL+X+1), (BAH, BAL+X)]}

IND

INDIRECT: The byte following the opcode is used as a pointer to the zero page. The

contents of this address and the following one are used as the address to finally access

the data. {data=[(IAL+1), (IAL)]}

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