80C451 Datasheet, PDF (5/22 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 4K/128 OTP/ROM/ROMless, expanded I/O

Philips Semiconductors
80C51 8-bit microcontroller family
4K/128 OTP/ROM/ROMless, expanded I/O
Product specification
80C451/83C451/87C451
PIN DESCRIPTION
MNEMONIC
PIN
NO.
V_SS
V_CC
P0.0–0.7
54
18
17-10
P1.0–P1.7
27-34
P2.0–P2.7
2-9
P3.0–P3.7
P4.0–P4.7
P5.0–P5.7
P6.0–P6.7
36-43
36
37
38
39
40
41
42
43
26-19
44-51
59-66
ODS
55
IDS
56
BFLAG
57
AFLAG
58
RST
35
ALE/PROG
68
PSEN
67
EA/V_PP
1
XTAL1
53
XTAL2
52
TYPE NAME AND FUNCTION
I
Ground: 0V reference.
I
Power Supply: This is the power supply voltage for normal, idle, and power-down operation.
I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 is also the multiplexed data and low-order
address bus during accesses to external memory. External pull-ups are required during program
verification. Port 0 can sink/source eight LS TTL inputs.
I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 receives the low-order
address bytes during program memory verification. Port 1 can sink/source three LS TTL inputs, and
drive CMOS inputs without external pull-ups.
I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 emits the high-order address
bytes during access to external memory and receives the high-order address bits and control signals
during program verification. Port 2 can sink/source three LS TTL inputs, and drive CMOS inputs without
external pull-ups.
I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 can sink/source three LS
TTL inputs, and drive CMOS inputs without external pull-ups. Port 3 also serves the special functions
listed below:
I
RxD (P3.0): Serial input port
O TxD (P3.1): Serial output port
I
INT0 (P3.2): External interrupt
I
INT1 (P3.3): External interrupt
I
T0 (P3.4): Timer 0 external input
I
T1 (P3.5): Timer 1 external input
O WR (P3.6): External data memory write strobe
O RD (P3.7): External data memory read strobe
I/O Port 4: Port 4 is a 8-bit (LCC) bidirectional I/O port with internal pull-ups. Port 4 can sink/source three
LS TTL inputs and drive CMOS inputs without external pull-ups.
I/O Port 5: Port 5 is a 8-bit (LCC) bidirectional I/O port with internal pull-ups. Port 5 can sink/source three
LS TTL inputs and drive CMOS inputs without external pull-ups.
I/O Port 6: Port 6 is a specialized 8-bit bidirectional I/O port with internal pull-ups. This special port can
sink/source three LS TTL inputs and drive CMOS inputs without external pull-ups. Port 6 can be used in
a strobed or non-strobed mode of operation. Port 6 works in conjunction with four control pins that
serve the functions listed below:
I
ODS: Output data strobe
I
IDS: Input data strobe
I/O BFLAG: Bidirectional I/O pin with internal pull-ups
I/O AFLAG: Bidirectional I/O pin with internal pull-ups
I
Reset: A high on this pin for two machine cycles while the oscillator is running, resets the device. An
internal pull-down resistor permits a power-on reset using only an external capacitor connected to V_CC.
I/O Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the address during
an access to external memory. ALE is activated at a constant rate of 1/6 the oscillator frequency except
during an external data memory access, at which time one ALE is skipped. ALE can sink/source three
LS TTL inputs and drive CMOS inputs without external pull-ups. This pin is also the program pulse
during EPROM programming.
O Program Store Enable: The read strobe to external program memory. PSEN is activated twice each
machine cycle during fetches from external program memory. However, when executing out of external
program memory, two activations of PSEN are skipped during each access to external program
memory. PSEN is not activated during fetches from internal program memory. PSEN can sink/source
eight LS TTL inputs and drive CMOS inputs without an external pull-up. This pin should be tied low
during programming.
I
Instruction Execution Control/Programming Supply Voltage: When EA is held high, the CPU
executes out of internal program memory, unless the program counter exceeds 0FFFH. When EA is
held low, the CPU executes out of external program memory. EA must never be allowed to float. This
pin also receives the 12.75V programming supply voltage (V_PP) during EPROM programming.
I
Crystal 1: Input to the inverting oscillator amplifier that forms the oscillator. This input receives the
external oscillator when an external oscillator is used.
O Crystal 2: An output of the inverting amplifier that forms the oscillator. This pin should be floated when
an external oscillator is used.
1998 May 01
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