5

1001E–MICRO–6/05

AT89C4051

6.

Special Function Registers

A map of the on-chip memory area called the Special Function Register (SFR) space is shown in

the Table 6-1.

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.

User software should not write 1s to these unlisted locations, 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.

Table 6-1.

AT89C4051 SFR Map and Reset Values

0F8H

0FFH

0F0H

B

00000000

0F7H

0E8H

0EFH

0E0H

ACC

00000000

0E7H

0D8H

0DFH

0D0H

PSW

00000000

0D7H

0C8H

0CFH

0C0H

0C7H

0B8H

IP

XXX00000

0BFH

0B0H

P3

11111111

0B7H

0A8H

IE

0XX00000

0AFH

0A0H

0A7H

98H

SCON

00000000

SBUF

XXXXXXXX

9FH

90H

P1

11111111

97H

88H

TCON

00000000

TMOD

00000000

TL0

00000000

TL1

00000000

TH0

00000000

TH1

00000000

8FH

80H

SP

00000111

DPL

00000000

DPH

00000000

PCON

0XXX0000

87H