The 8051 microcontrollers in EDWinXP help the users to build real-time circuits. The 8051 can be interfaced with external devices like seven segment displays, interrupt generator, serial/pattern generator etc.

Using the 8051 microcontroller in EDWinXP

1. Open EDWinXP Main from Start→ Programs→ EDWinXP →Ver x.xx→ EDWinXP Main.
2. Open the Schematic Page (Mixed-Mode Simulator) by double clicking on the Page {MAIN PAGE} under Project→ Circuit [MAINHIER] →Diagram→ Page {MAIN PAGE}.
3. Load 8051 microcontroller and Preprocess it.
4. The necessary timing for the controller is given by connecting a crystal across the pins XTAL1 and XTAL2. The timing can be provided manually by applying a clock of the desired frequency of the crystal to the pin XTAL1/XTAL2. This is done by selecting Tools→ Instruments → Preset Logic → Clock Generator
5. Connect nodes on XTAL1/XTAL2
6. Now by clicking on either of the two nodes XTAL1/XTAL2 the following window appears

7. Provide the desired frequency,
    Eg: if the crystal frequency is 6MHz, then the time period will be (1)/(6x10 6 ) i.e. 0.1667 x10¯ 6
The clock fed to the XTAL pin is {L1us, H1us} as Repeatable Pattern
8. Click on Add → Set Pattern → Accept

Writing code for 8051 microcontroller

1. Select Components from the Tool Menu.
2. Choose Component Properties (second Function tool) → Change Simulation parameters (second option tool) and Click on the 8051 microcontroller. A new window pops up.

3. Click Setup tab, the code editor window pops up. Code can be written in this window. Code can be written either in C language or assembly language.

The tool bar in the code editor window is shown below

Clear text	Clears the source code in the code editor window
Import from disk	Displays the ‘Open’ dialog box and allows loading a new text file
Save	Allows to save the source code.
Export to disk	Displays the ‘Save’ dialog box and allow to save the source code.
Build	Enables compilation of the source code.
Start Debug	Enters the Debug mode.
Stop Debug	Terminates debug mode.
Step over	Generates an event to notify model to step over the currently debugged part of the code.
Step into	Enables to view the line by line execution of the source code in debug mode.

Writing source code in C language

Basic structure for writing code in C language is

#include<8051.h>
void main ()
{
}

The code is written within the main () function. For better understanding, the case of 8051_Counter is taken. Load 8051_Counter and the steps mentioned till now in Writing code for 8051 microcontroller are executed.

The code for 8051_Counter is as follows:

By compiling (using the Build button) the basic structure in the C Editor, the default structure in the Assembly Editor will be obtained.

The code is written within the _main function. The location to write the code is shown in the figure below.

The code in Assembly Editor is also compiled by using the Build button in the code editor Window.
Compilation messages will be shown under the Line Message column.
After successful compilation click the Save button and close the code editor window. Click Accept in the Component Parameter Setup window.
After completing the schematic the circuit is Preprocessed and Analysis is Run.

Debugging the code

Place breakpoints to keep track of program execution.
Breakpoints can be placed by clicking on the gray space on left of the code statements.

Click on Start Debug button in the code editor window. This will turn on the debug mode.
Close the Code Editor window and click Accept in Component Parameter Setup.
Go to Schematic Editor and Run Analysis, the code editor window pops up.
The program can be debugged using the Step Over (switching between breakpoints) and Step Into (step by step execution) buttons.
By clicking on the required ports and registers the changes in them can be viewed during the process.

After debugging the Stop debug button is clicked to exit the Debug mode. The Analysis continues till simulation time ends.