xr88c681 Exar Corporation, xr88c681 Datasheet - Page 25

• Manufacturer Part Number: xr88c681
• Description: Cmos Dual Channel Uart Duart
• Manufacturer: Exar Corporation

The 8051 C consists of 4 8-bit I/O ports. Some of these
ports have alternate functions, as will be discussed here.
Port 0 (P0.0 - P0.7)
This port is a dual-purpose port on pins 32 - 39 of the 8051
IC. In minimal component designs, it is used as a general
purpose I/O port.
memory, it becomes a multiplexed address and data bus
(AD0 - AD7).
Port 2 (P2.0 - P2.7)
Port 2 (Pins 21 - 28) is a dual-purpose port that can
function as general purpose I/O, or as the high byte of the
Rev. 2.11
For larger designs with external
P3.3 (-INT1)
P3.2 (-INT0)
P3.0 (RXD)
P3.1 (TXD)
P3.6 (-WR)
P3.7 (-RD)
P3.4 (T0)
P3.5 (T1)
XTAL1
Figure 4. Pin Out of the 8051 Microcontroller
XTAL2
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
RST
V
SS
10
11
12
15
18
19
13
14
16
17
20
4
1
2
3
5
6
7
8
9
Microcontroller
8051
25
Port 1 (P1.0 - P1.7)
Port 1 is a dedicated I/O port on pins 1 - 8. The pins,
designated as P1.0, P1.1, P1.2, ..., are available for
interfacing as required.
assigned for Port 1 pins; thus they are used solely for
interfacing to external devices.
8032/8052 ICs, which use P1.0 and P1.1 either as I/O
lines or as external inputs to the third timer.
address bus for designs with external code memory of
more than 256 bytes of external data memory (A8 - A15).
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
V
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
-EA
ALE
-PSEN
P2.7 (A15)
P2.6 (A14)
P2.5 (A13)
P2.4 (A12)
P2.3 (A11)
P2.2 (A10)
P2.1 (A9)
P2.0 (A8)
CC
No alternative functions are
XR88C681
Exceptions are the