Special
Function
Registers
A map of the on-chip memory area called the Special Function Register (SFR) space is shown
in Table 1.
Note that not all of the addresses are occupied, and unoccupied addresses may not be imple-
mented on the chip. Read accesses to these addresses will in general return random data,
and write accesses will have an indeterminate effect.
Table 1. AT89S51 SFR Map and Reset Values
0F8H
0FFH
0F7H
0EFH
0E7H
0DFH
0D7H
0CFH
0C7H
0BFH
0B7H
0AFH
0A7H
9FH
B
0F0H
00000000
0E8H
ACC
0E0H
00000000
0D8H
PSW
0D0H
00000000
0C8H
0C0H
IP
0B8H
XX000000
P3
0B0H
11111111
IE
0A8H
0X000000
P2
11111111
AUXR1
XXXXXXX0
WDTRST
XXXXXXXX
0A0H
98H
90H
88H
80H
SCON
00000000
SBUF
XXXXXXXX
P1
11111111
97H
TCON
00000000
TMOD
00000000
TL0
00000000
TL1
00000000
TH0
00000000
TH1
00000000
AUXR
XXX00XX0
8FH
P0
11111111
SP
00000111
DP0L
00000000
DP0H
00000000
DP1L
00000000
DP1H
00000000
PCON
0XXX0000
87H
6
AT89S51
2487B–MICRO–12/03
ATMEL [ ATMEL ]
