AT89C2051 I/O Port Programming in C

Note: In this series of tutorial, I am assuming that you already have a basic knowledge about programming using C language.

Some of the registers of AT80C2051 are byte accessible or  bit accessible. A byte access to a register means that the whole register, if it is byte wide, is accessed at a single time. A bit access to a register means that only a single bit inside a register is accessed at a time.

The ports of AT89C2051 can be byte accessible or  bit accessible. Typically, writing FF(hex) to P1(a register/port) is the same as writing 1′s to each of the pins or bits of P1 (from P1.0 to P1.7).

For example,

P1 = 0xFF; //write FF hex to P1

is the same as

P1^0 = 1;
P1^1 = 1;
P1^2 = 1;
P1^3 = 1;
P1^4 = 1;
P1^5 = 1;
P1^6 = 1;
P1^7 = 1;

Similarly, reading the ports of AT89C2051 can be done through byte access or as bit access.

unsigned char temp; //creating a byte-size variable named temp

bit my_flag; //creating a bit-size variable named my_flag

temp = P1; //reading the value of P1 and saving it to temp

my_flag = P3^0; //reading the value of P3.0 and saving it to my_flag

 note: bit and unsigned char are data types

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