P3.5 (T1)
P3.6 (/WR)
P3.7 (/RD)
15
16
17
17
18
19
11
12
13
keep the port high. Port3 also serves
other special functions of this device.
P3.0 and P3.1 act as receiver and
transceiver of the data for UART function
block,
Alias RXD and TXD.
P3.2 and P3.3 also act as external
interrupt sources, alias INT0 and INT1.
P3.4 and P3.5 also act as event sources
for timer0 and timer1 individually, alias
T0 and T1.
P3.6 also acts as write signal while
access to external memory, alias /WR.
P3.7 also acts as read signal while
access to external memory, alias /RD.
P4.0
P4.1
P4.2 (/INT3)
P4.3 (/INT2)
RESET
ALE
9
30
23
34
1
12
10
33
17
28
39
6
4
27
BU Port4 is extended I/O ports such like
Port1. It can be available only on
44L-PLCC and 44L-PQFP package.
IS
O
A high on this pin for at least two
machine cycles will reset the device.
Output pulse for latching the low bytes of
address during accesses to external
memory.
/PSEN
/EA
29
31
32
35
26
29
O
I
The read strobe to external program
memory, low active.
EA must be kept at low to enable the
device to fetch program code from
external flash memory.
An internal pull-up resistance has been
embedded in this pin.
XTAL1
XTAL2
VDD
VSS
19
18
40
20
21
20
44
22
15
14
38
16
I
O
P
G
Input to the inverting oscillator amplifier.
Output from the inverting amplifier.
Power Supply
Ground
MEGAWIN
MPC89x51A Data Sheet
5
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
