XR88C681_06 Datasheet, PDF (25/101 Pages) Exar Corporation – CMOS Dual Channel UART (DUART)

XR88C681
P1.0 1
P1.1 2
P1.2 3
P1.3 4
P1.4 5
P1.5 6
P1.6 7
P1.7 8
RST 9
P3.0 (RXD) 10
P3.1 (TXD) 11
P3.2 (-INT0) 12
P3.3 (-INT1) 13
P3.4 (T0) 14
P3.5 (T1) 15
P3.6 (-WR) 16
P3.7 (-RD) 17
XTAL2 18
XTAL1 19
V_SS 20
8051
Microcontroller
40 V_CC
39 P0.0 (AD0)
38 _{P0.1 (AD1)}
37 P0.2 (AD2)
36 P0.3 (AD3)
35 P0.4 (AD4)
34 P0.5 (AD5)
33 P0.6 (AD6)
32 P0.7 (AD7)
31 -EA
30 ALE
29 -PSEN
28 P2.7 (A15)
27 P2.6 (A14)
26 _{P2.5 (A13)}
25 P2.4 (A12)
24 P2.3 (A11)
23 P2.2 (A10)
22 P2.1 (A9)
21 P2.0 (A8)
Figure 4. Pin Out of the 8051 Microcontroller
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. For larger designs with external
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
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. No alternative functions are
assigned for Port 1 pins; thus they are used solely for
interfacing to external devices. Exceptions are the
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).
Rev. 2.11
25