DETAILS:
The ATMEL 89C51 is a low power, high performance CMOS 8-bit microcontroller with 4K bytes of In System Programmable Flash Memory. It is suitable for cost effective embedded systems.
It has following standard features:
4K bytes of flash memory, 128 bytes of RAM, 32 I/O pins, two 16 bit timers/counters, a full duplex serial port, on chip oscillator, and clock circuitry, six interrupt sources, standard 40 pin package, external memory interface.
RST:
This is the reset input. This input should normally be at logic 0. A reset is accomplished by holding the RST pin for at least two machine cycles. Power-on reset is normally performed by connecting an external capacitor and a resistor this pin.
P3.0:
This is bi-directional I/O pin with an interrupt pull-up resistor. This pin also acts as the data receive input (RXD) when using the device as serial data.
P3.1:
This is bi-directional I/O pin with an internal interrupt pull-up resistor. This pin also acts as the data transmit output (TXD) when sending serial data.
XTAL1 and XTAL2:
These pins are where external crystal oscillator should be connected for the operation of the internal oscillator. Normally two 33pF capacitors are connected with the crystal as shown. A machine cycle is obtained by dividing the crystal frequency by 12. Thus, with a 12MHz crystal, the machine cycle is 1us. Most machine instructions execute in one machine cycle.
P3.3:
This is a bi-directional I/O pin. This pin also is the external interrupt (INT1) pin.
P3.4:
This is bi-directional pin. This pin is also used for the counter 0 input (TO) pin.
P3.5:
This is bi-directional pin. This is also used for counter 1 input (T1) pin.
GND:
It is the ground pin.
P3.6:
This is bi-directional pin. It is also the external memory write (WR) pin.
P3.7:
This is bi-directional pin. This pin is also the external data memory read (RD) pin.
P1.0:
This is bi-directional pin. It has no internal pull-resistors. P1.1:
This is bi-directional pin. It has no internal pull-up resistors.
P1.2 to P1.7:
These are remaining bi-direction pins. These pins have internal pull-up resistors.
VCC:
It is the supply voltage. 5V is supplies here.
P0.0 to P0.7:
These are eight I/O pins. These have no internal pull-up resistors.
P2.0 to P2.7:
These are the eight I/O pins. These have internal pull-up resistors.
EA/VPP:
This is the external access enable pin on the 8051. EA should be connected to VCC for internal programme executions. This pin also receives the programming voltage during programming.
PSEN:
This is the programme store enable pin. This is used when using external memory.
ALE/PROG:
This is the address latch enable pin.
The ATMEL 89C51 is a low power, high performance CMOS 8-bit microcontroller with 4K bytes of In System Programmable Flash Memory. It is suitable for cost effective embedded systems.
It has following standard features:
4K bytes of flash memory, 128 bytes of RAM, 32 I/O pins, two 16 bit timers/counters, a full duplex serial port, on chip oscillator, and clock circuitry, six interrupt sources, standard 40 pin package, external memory interface.
RST:
This is the reset input. This input should normally be at logic 0. A reset is accomplished by holding the RST pin for at least two machine cycles. Power-on reset is normally performed by connecting an external capacitor and a resistor this pin.
P3.0:
This is bi-directional I/O pin with an interrupt pull-up resistor. This pin also acts as the data receive input (RXD) when using the device as serial data.
P3.1:
This is bi-directional I/O pin with an internal interrupt pull-up resistor. This pin also acts as the data transmit output (TXD) when sending serial data.
XTAL1 and XTAL2:
These pins are where external crystal oscillator should be connected for the operation of the internal oscillator. Normally two 33pF capacitors are connected with the crystal as shown. A machine cycle is obtained by dividing the crystal frequency by 12. Thus, with a 12MHz crystal, the machine cycle is 1us. Most machine instructions execute in one machine cycle.
P3.3:
This is a bi-directional I/O pin. This pin also is the external interrupt (INT1) pin.
P3.4:
This is bi-directional pin. This pin is also used for the counter 0 input (TO) pin.
P3.5:
This is bi-directional pin. This is also used for counter 1 input (T1) pin.
GND:
It is the ground pin.
P3.6:
This is bi-directional pin. It is also the external memory write (WR) pin.
P3.7:
This is bi-directional pin. This pin is also the external data memory read (RD) pin.
P1.0:
This is bi-directional pin. It has no internal pull-resistors. P1.1:
This is bi-directional pin. It has no internal pull-up resistors.
P1.2 to P1.7:
These are remaining bi-direction pins. These pins have internal pull-up resistors.
VCC:
It is the supply voltage. 5V is supplies here.
P0.0 to P0.7:
These are eight I/O pins. These have no internal pull-up resistors.
P2.0 to P2.7:
These are the eight I/O pins. These have internal pull-up resistors.
EA/VPP:
This is the external access enable pin on the 8051. EA should be connected to VCC for internal programme executions. This pin also receives the programming voltage during programming.
PSEN:
This is the programme store enable pin. This is used when using external memory.
ALE/PROG:
This is the address latch enable pin.
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