The document discusses digital I/O programming on microcontrollers, including how to access different ports, avoid issues with ports 0 and 3, and use keywords like sbit, sfr, and bit to directly access I/O ports and registers to set inputs and outputs as well as create software delays for applications like displaying a Fibonacci series using LEDs.

1. DIGITAL I/O

2. I/O Programming 4 ports for I/o Programming Port 0 0x80 Port 1 0x90 Port 2 0xA0 Port 3 0xB0

3. Secret of Port 0 Port 0 has no pull up resistors Reason? Due to the purpose of Port 0 as data and address holder , it cannot have a resistor in the output pins. By directly giving the supply of 5 v to the port 0 will damage the internal transistor eventually. Solution : By connecting external pull up resistor in a range of 1K to 10K ohms , the damage to the internal transistor can be avoided.

4. Try to Avoid Port 3 Port 3 is also called as multifunctional port. It is used for serial communication, timer, external interrupt, chip read and write. Therefore by using port 3 in a situation under which a serial communication or connecting an external memory which will cause loss of data or misbehavior in the output. Also the timer and interrupts are very sensitive to the crystal frequency.

5. Remaining for I/O programming The remaining for I/O programming are Port 1 and Port 2 only. Port 1 is a simple bidirectional Port Port 2 is also a bidirectional with MSB of 16 bit address Remember that port 2 is in reverse order while looking aerially

6. C programming of I/Os Key word for accessing I/Os sbit a single bit ---------| sfr eight bit ____ |----- for accessing I/O directly bit a single bit-----|----| sfr 16 16 bit-----------|-----------for acessing I/O indirectly

7. Giving to Ports & Getting from the Ports You can set a particular port with the help of the keyword “ sbit” Eg., sbit my_key =P1^1; Explanation: my_key is the user defined variable which can be used to get or send data to 2 nd PIN of Port 1. ^ symbol is used to mention a particular PIN any port

8. Use of bit “ bit ” is another single bit keyword which is used to change the value for the variable which is assigned by the sbit keyword. Rather we can simply use it for “Boolean operation”. Eg., bit garbage; garbage =1; while(1) { garbage = ~garbage; my_key = garbage } Explanation: garbage is a user defined variable which can only be used as either ‘0’ or ‘1’

9. Sfr made for?? “ sfr ” is an eight bit keyword, which allows user to set a 8-bit value. Most of the registers in uC are 8-bit registers. Therefore it is easy to use all 8-bit register using the “ sfr ” keyword. Eg., sfr myport=0x80; Explanation: Here myport is a user defined variable which is assigned to get or send value through PORT 0 (since port 0 is located in 0x80 address). This is not only for ports, but also all register(TCON, SBUF, PCON, etc.,) can be assessed like this.

10. What about 16-bit registers??? Still there are some registers which have 16-bit . Therefore to access those 16-bit registers, sfr16 has to be used. The only 16-bit register which can be often used is DataPoinTeR (DPTR) sfr16 can be used to assign that DPTR register.

11. Delay is the main concept.. After the infinite loop concept, Delay is another important thing in the embedded system. There are different type of delays available in microcontroller By using the I/O concept delay can be produced. Basic of delay is no operation for a particular period. Here we providing that concept via programming Therefore we can call this kind of delays as “ software delays ”

12. Simple delay program int i,j; for(i=0;i<250;i++) { for(j=0;j<1275;j++) { ; } } This will generate approximately 1 sec delay. Software delays are only approximate figures.

13. A simple I/O programming #include<reg51.h> sbit book = P1^2; //port 1 – 3 rd pin sfr select =P0; //port 0 void main() { book=1; // as an input bit name =1; // single bit declaration while(1) { if(book==1) // condition check in port 1 – 3 rd pin { book=~name; //changing the value for book Select=0x55; //sending the output to port 0 } } }

14. Try to do an arithmetic operation using I/O concept. Do a Fibonacci series using delay and I/O concept Made a Boolean table for any logic operation