Special Function Registers
A map of the on-chip memory area called the Special Func-
tion Register (SFR) space is shown in the table below.
User software should not write 1s to these unlisted loca-
tions, since they may be used in future products to invoke
new features. In that case, the reset or inactive values of
the new bits will always be 0.
Note that not all of the addresses are occupied, and unoc-
cupied addresses may not be implemented on the chip.
Read accesses to these addresses will in general return
random data, and write accesses will have an indetermi-
nate effect.
Table 1. AT89C2051 SFR Map and Reset Values
0F8H
0FFH
0F7H
0EFH
0E7H
0DFH
0D7H
0CFH
0C7H
0BFH
0B7H
0AFH
0A7H
9FH
0F0H
0E8H
0E0H
0D8H
0D0H
0C8H
0C0H
0B8H
0B0H
0A8H
0A0H
98H
B
00000000
ACC
00000000
PSW
00000000
IP
XXX00000
P3
11111111
IE
0XX00000
SCON
SBUF
00000000
XXXXXXXX
90H
P1
97H
11111111
88H
TCON
00000000
TMOD
00000000
TL0
00000000
TL1
00000000
TH0
00000000
TH1
00000000
8FH
87H
80H
SP
DPL
DPH
PCON
00000111
00000000
00000000
0XXX0000
AT89C2051
4-18
ATMEL [ ATMEL ]
