IS89C52
Table 1. Detailed Pin Description
Symbol
ALE/
PROG
PDIP
30
PLCC
33
PQFP
27
I/O
I/O
Name and Function
ISSI
®
EA
/V
PP
Address Latch Enable:
Output pulse for latching the low byte
of the address during an address to the external memory. In
normal operation, ALE is emitted at a constant rate of 1/6 the
oscillator frequency, and can be used for external timing or
clocking. Note that one ALE pulse is skipped during each
access to external data memory. This pin is also the Program
Pulse input (
PROG
) during Flash programming.
31
35
29
I
External Access enable:
EA
must be externally held low to
enable the device to fetch code from external program memory
locations 0000H to FFFFH. If
EA
is held high, the device
executes from internal program memory unless the program
counter contains an address greater than 0FFFH. This also
receives the 12V programming enable voltage (V
PP
) during
Flash programming.
Port 0:
Port 0 is an 8-bit open-drain, bidirectional I/O port. Port
0 pins that have 1s written to them float and can be used as high-
impedance inputs. Port 0 is also the multiplexed low-order
address and data bus during accesses to external program and
data memory. In this application, it uses strong internal pullups
when emitting 1s.
Port 0 also receives the code bytes during programmable
memory programming and outputs the code bytes during
program verification. External pullups are required during pro-
gram verification.
Port 1:
Port 1 is an 8-bit bidirectional I/O port with internal
pullups. Port 1 pins that have 1s written to them are pulled high
by the internal pullups and can be used as inputs. As inputs,
Port 1 pins that are externally pulled low will source current
because of the internal pullups. (See DC Characteristics: I
IL
).
The Port 1 output buffers can sink/source four TTL inputs.
Port 1 also receives the low-order address byte during Flash
programming and verification.
P0.0-P0.7
39-32
43-36
37-30
I/O
P1.0-P1.7
1-8
2-9
40-44
1-3
I/O
1
2
P2.0-P2.7
21-28
2
3
24-31
40
41
18-25
I
I
I/O
T2(P1.0):
Timer/Counter 2 external count input.
T2EX(P1.1):
Timer/Counter 2 trigger input.
Port 2:
Port 2 is an 8-bit bidirectional I/O port with internal
pullups. Port 2 pins that have 1s written to them are pulled high
by the internal pullups and can be used as inputs. As inputs,
Port 2 pins that are externally pulled low will source current
because of the internal pullups. (See DC Characteristics: I
IL
).
Port 2 emits the high order address byte during fetches from
external program memory and during accesses to external data
memory that used 16-bit addresses (MOVX @ DPTR). In this
application, Port 2 uses strong internal pullups when emitting
1s. During accesses to external data memory that use 8-bit
addresses (MOVX @ Ri [i = 0, 1]), Port 2 emits the contents of
the P2 Special Function Register.
Port 2 also receives the high-order bits and some control
signals during Flash programming and verification. P2.6 and
P2.7 are the control signals while the chip programs and
erases.
Integrated Silicon Solution, Inc. — 1-800-379-4774
MC013-1C
11/21/98
5
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
