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Pins 1 to 8(Port 1): The Pins 1.0 to 1.7 are 8 Pins of port 1. Each of them can be configured as input or output pin.
Pin 9: It is used to Reset Microcontroller 8051. A positive pulse is given on this Pin to reset Microcontroller.
Pin 10 to 17(Port 3): These Pins are similar to Pins of Port 1. These Pins can be used as universal Input or output. These are dual function Pins. Function of each Pin is given as:
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- Pin 10:It is Serial Asynchronous Communication Input or Serial Asynchronous Communication Output.
- Pin 11: Serial Asynchronous Communication Output or Serial Synchronous Communication Output.
- Pin 12: Interrupt 0 input.
- Pin 13: Interrupt 1 input.
- Pin 14: Counter 0 clock input.
- Pin 15: Counter 1 clock input.
- Pin 16: Writing Signal for Writing content on external RAM.
- Pin 17: Reading Signal to read contents of external RAM.
- Pin 18 and 19: These are input output PINS for oscillator. An internal oscillator is connected to Micro controller through these PINS.
- Pin 20: Pin 20 is grounded.
- Pin 21 to 28 (Port 2):These Pins can be configured as Input Output Pins. But this is only possible in case when we don't use any external memory. If we use external memory then these pins will work as high order address bus(A8 to A15).
- Pin 29: If we uses an external ROM then it should has a logic 0 which indicates Micro controller to read data from memory.
- Pin 30: This Pin is used for ALE that is Address Latch Enable. If we uses multiple memory chips then this pin is used to distinguish between them. This Pin also gives program pulse input during programming of EPROM.
- Pin 31: If we have to use multiple memories then by applying logic 1 to this pin instructs Micro controller to read data from both memories first internal and afterwards external.
- Pin 32 to 39(Port 0): Similar to port 2 and 3, these pins can be used as input output pins when we don't use any external memory. When ALE or Pin 30 is at 1 then this port is used as data bus, when ALE pin at 0, then this port is used as lower order address bus(A0 to A7).