Hello Readers:
I have started this blog to show you Embedded C programming for 8051 family microcontroller using KEIL compiler. The KISS philosophy is used to write this tutorial. What is KISS? Keep It Simple, Stupid!
2.1 Bytewise [all port pins-8bits]
The third program you are going to write is showing 0 to 255 numbers, in binary form on output port P2 with rough delay using for loop. It is mandatory for a programmer to learn to write reusable optimized delay functions. This teaches you how to write rough delay using for loop structure and put it in suitable function.
Code explanation: The program uses for loop structure to send numbers 0 to 255 [0 to FFxh] to Port 2 [line 11]. The variable used [line 09] to send is of type unsigned char as it needs one byte memory only [where as int needs 2 bytes]. Inside for loop [line 11] z, a unsigned char variable is initialized to zero. The ‘z<=255’ instruction checks whether z is less than or equal to 255 or not. If it is then zero is send to Port 2 [line 13] and increments z. Now z is 1 and after validation is send to Port 2. Again z is incremented, and above steps is repeated. When z value reaches 256, validation goes wrong, as it is not less than or equal to 255 [z is greater than 255] and hence for loop terminates [line 15]. Since there are no other codes to executes [line 16], compiler reinitializes the for loop [line 11] and continues the same thing repeatedly.
Inside a for loop rDelay() function is added [line 14] after sending Port 2 value to keep some delay between value outputs. The compiler starts executing the code from top and when it comes to line 14 it stops as it does not know what it is. So it is necessary to declare or prototype the function before its use. In line 05 delay function is prototyped, that means it is declared before main() function [line 07] execution.
The rough delay rDelay() function contains unsigned int i variable. Now variable used is unsigned int as we need 2 bytes of value [not single byte]. This i is initialized to zero [line 20] and checked inside the for loop structure [line 22] for validation. Here i variable is checked whether it is less than or equal to 65435 or not. If not then just increment i and check for validation. Here doing nothing is indicated by semicolon ‘;’ as shown on line 22. These steps are repeated until i becomes 65435 and for next step for loop structure breaks out. Since there are no further codes to execute rDelay() function comes out. Thus this rDelay() function produces rough delay of some milliseconds [which differs with chip and compiler type]
After typing the code, press F7 or click Project->Build Target for building the source code. If there are no typical errors file will build successively and shows zero errors and zero warnings.
Now enter into debug mode by pressing Ctrl+F5 or click Debug->Start/Stop Debug Session menu. Our program is sending 0 to 255 numbers in binary form to Port 2 continuously. So we want to watch the Port 2 pins while running this program for changing values. To get Port 2 tab click Peripherals->I/O Ports->Port 2 text.
Run the program by pressing F5 or clicking Debug->Run. You can see the changing values from 0 to 255 on Port 2 tab continuously in binary form. If you generate HEX file of this program, burn it into your target chip’s memory using suitable uploader and connecting 8 LEDs to Port 2 you can watch LEDs blinking in binary form. To stop running the program press red ‘x’ mark icon or click Debug->Stop.
...till next post bye-bye & take care.
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