S
un
pl
us
IT
C
on
fid
en
tia
l
F
or
A
D
D
In
te
rn
at
io
na
l L
im
ite
d
U
se
O
nl
y
CPU6502 Instruction Manual v2.1
Sunplus reserves the rights to change this documentation without prior notice.
09/13/2005
8
Register
7 0
A
Accumulator
7 0
X
Index Register X
7 0
Y
Index Register Y
15 8
7 0
PCH
PCL
Program Counter
7 0
SP
Stack Pointer
7 0
P
Status Register
Register Size
Description
Accumulator (A)
8 Bit Accumulator is the only register that can be used for arithmetic or
logic operation such as ADD, SUB, AND, OR and EOR and store
the result in it.
Index Register X
8 Bit X is an index register which can be used as a memory buffer, a
offset, or a counter.
Index Register Y
8 Bit Y is an index register which can be used as a memory buffer, a
offset, or a counter.
Program
Counter(PC)
16 Bit PC is a 16-bit register. Program Counter points to an address
location where an instruction is held and waits to be executed by
CPU next. When CPU fetches one instruction to execute, PC is
incremented to the next location in memory from which the next
instruction to be executed will be taken unless a branch is
occurred that will lead PC points to the specified address location.
Stack Pointer(SP)
8 Bit Stack Pointer is an 8-bit register. Normally, SP is used for
storing return address, data of status register or temporary data.
Status Register (P) 8 Bit Status Register usually offers information on result of previous
instruction executed.
