FMA Unit 1.3 8051 microcontroller PIN Diagram

• Pins 1 to 8 (Port 1) –This port doesn’t serve any other functions. It is internally pulled up, bi-directional I/O port.
• Pin 9 (RST) − It is a RESET pin, which is used to reset the microcontroller to its initial values.

·         Pins 10 to 17 (Port 3) − This port serves some functions.

ü Pin 10 (RXD): It is a Serial Communication Input.

ü Pin 11 (TXD): It is a Serial Communication output

ü Pin 12 (): Input of Interrupt 0

ü Pin 13 (): Input of Interrupt 1

ü Pin 14 (T0): Input of Counter 0 clock

ü Pin 15 (T1): Input of Counter 1 clock

ü Pin 16 (): Writing Signal to write content on external RAM.

ü Pin 17 (): Reading Signal to read contents of external RAM.

• Pin 18 (XTAL2) and Pin 19 (XTAL1) − These pins are used for interfacing an external crystal to get the system clock.
• Pin 20 (GND) − It is ground pin.
• Pins 21 to 28 − These pins are known as Port 2. It can be configured as Input Output Pins. But, this is only possible when  any external memory not used. If we use external memory, then these pins will work as high order address bus (A8 to A15).
• Pin 29 − This pin is used to enable external program memory. If we use an external ROM for storing the program, then logic 0 appears on it.

·         Pin 30  − This is the Address Latch Enable Pin. Using this Pins, external address can be separated from data (as they are multiplexed by 8051).During Flash Programming, this pin acts as program pulse input (PROG).

·        Pin 31 – This is the External Access Enable Pin i.e. allows external Program Memory. During Flash Programming, this Pin receives 12V Programming Enable Voltage (VPP).

• Pins 32 to 39 − These pins are known as Port 0. These pins can be used as input output pins when any external memory not used. When ALE or Pin 30 is at 1, then this port is used as data bus: when the ALE pin is at 0, then this port is used as a lower order address bus (A0 to A7)
• Pin 40 − This pin is used to provide power supply to the circuit.

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