4x4 matrix keypad c code for pic16f877a

4x4 matrix keypad c code for pic16f877a

This button keypad provides a useful human interface component for micro controller projects. Convenient adhesive backing provides a simple way to mount the keypad in a variety of applications. Matrix keypads use a combination of four rows and four columns to provide button states to the host device, typically a micro-controller.

Underneath each key is a push button, with one end connected to one row, and the other end connected to one column. In order for the micro-ocontroller to determine which button is pressed, it first needs to pull each of the four column either low or high one at a time, and then poll the states of the four rows. Depending on the states of the rows, the micro controller can tell which button is pressed. Additional 4 of 10k ohm resistors were used to pull out the 4 columns of the keypad.

However, DIY scanning of keypad consumes a lot of understanding in programming and more program space. The better way to interface a keypad to the PIC is to use a keypad encoder in between the keypad and the microcontroller. Simply hook up all the row and the column pins directly to the encoder and it will output a HIGH pulse on the Data Available pin whenever a key is pressed. After that, the encoder will output 4 bits of data to the PIC.

It will test whether the 1st row of the keypad being pressed or not. If not, it will goto to 2nd row to check for the button pressed. If the button of the 1st row was being pressed, it will test which column is the location. Same go to column 3 and 4.

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If the keypad does not being pressed, this function will return 0xFF to the function which will used it. The led will be toggle each time for the button of the keypad being pressed.

The LCD will display the character of the keypad as you pressed the button. I used to be looking for this certain information for a very lengthy time. Thanks and good luck. My hardware layout is identical. Also, the file keypad. Thanks in advance. Resistors need only be. Error pop pup in output shown like below this text. In this tutorial, you will learn on how to display the character on LCD by pressing the 4x4 keypad button.

Male to Male Jumper Wire. Leave a Comment Cancel Reply Your email address will not be published.AlgorithmInterfaceTheory. In this post we will discuss logic and interface of a matrix keypad 4x4 for this post with microcontroller to reduce the number of port pins required to read a certain number of inputs digital. The same logic applies to any matrix keypad of order NxN.

Where, N is the order of the matrix. Typically one port pin is required to read a digital input into the controller. When there are a lot of digital inputs that have to be read, it is not feasible to allocate one pin for each of them. This is when a matrix keypad arrangement is used to reduce the pin count. Therefore, the number of pins that are required to interface a given number of inputs decreases with increase in the order of the matrix.

Example: If the matrix is 2x2, you will need 2 pins for the rows and 2 pins for the columns. In such a case there is no difference in the cost of reading that many inputs. But if you consider a 10x10 matrix you will just need 20 pins 10 for the rows and 10 for the columns to read digital inputs.

From the circuit you can see that when one of the 16 buttons are pressed, a pair of pins are connected together. We will use this feature to detect the button that was pressed in the following sections.

Initially all switches are assumed to be released. So there is no connection between the rows and columns. When any one of the switches are pressed, the corresponding row and column are connected short circuited.

This will drive that column pin initially high low. Using this logic, the button press can be detected. The colors red and black is for logic high and low respectively. Here are the steps involved in determining the key that was pressed. In the image, black line symbolizes logic 0 and red line symbolizes logic 1. For now let us assume that, the circled key is pressed and see how the key press can be detected by a software routine. Now the software has to scan the pins connected to columns of the keypad.

If it detects a logic 0 in any one of the columns, then a key press was made in that column. This is because the event of the switch press shorts the C2 line with R2. Hence C2 is driven low. The logic is that if a button in that row was pressed, then the value written to that row will be reflected in the corresponding column C2 as they are short circuited. Note: color of the lines indicate the logic values they return.

The procedure is followed till C2 goes high when logic high is written to a row.

PIC16F877A – Keypad Interfacing

In this case, a logic high to the second row will be reflected in the second column. We already know that the key press happened at column 2. Now we have detected that the key is in row 2.

So, the position of the key in the matrix is 2,2.Frank Donald August 29, 4 Comments. PIC tutorials. LCDmicrocontrollerswitches. Interfacing LCD and Keypad are one of the important interfacing concepts of PIC microcontroller since both the input and output element can form a complete embedded system design. This type of LCD is widely used to display the status of the system and to display the obtain output.

You have to follow these steps to write a command or data into the LCD.

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Still not clear about the working of LCD? The keypad was scanned for any key inputs and this was done by means of a method called polling. The scanning takes place by keeping a specific Row low at a time and read the status of the column pins as input at that instant.

This chain goes on through all the rows and by this way input is read by Microcontroller. What help you exactly need please?

4x4 matrix keypad c code for pic16f877a

Most reacted comment. Hottest comment thread. Recent comment authors. Notify of. Notify of all new follow-up comments Notify of new replies to all my comments. Frank Donald. Hi Rabah, Thanks for visiting.The Matrix keypad interfaces 16 keys to the microcontroller port using only 8 pins and a suitable firmware scans the pins for detecting the keypress. We have to look at the hardware part of the keypad before writing the firmware as the firmware logic depends on the hardware connections.

Similar to the General convention we will consider the horizontal connections as rows and the vertical connections as columns. The 16 keys can be arranged into rows and columns such that we can identify each key as a combination of row and column address similar to matrix element.

The input pins can be connected in a pull-up and pull-down mode. The default state of the input pins connected in pull-up mode will be high and similarly, in pull-down mode, it will be LOW. The programmer can set these conventions according to their convenience but it is important to match these conventions both in hardware and firmware.

4x4 matrix keypad c code for pic16f877a

Matrix keypad pinout will have a slight difference according to the manufacturer and please refer the datasheet for the pinout details of the keypad module you are using. You can also build the matrix keypad by arranging the switches in the matrix format as shown below. Let us consider the input pins connected in pull-up mode. The default state of input pins will be high in the pull-up mode. When a switch has pressed the column and row corresponding to the pressed key will be shorted and thus the value in the output line will be reflected in the input.

The logic low is written to one of the rows and other row pins will be kept high as in the case of pull up mode. We will continue this procedure and write a logic low to other row pins and check the columns pins to detect the keypress. We will have to connect the keypad to one of the controller ports. We have to create a function to detect the keypress.

You have to connect the inputs in either pullup or pull down mode. We will consider the pull-up mode here and the default input states will be high. When a key has pressed the row and column of that key will be shorted and the row value will be reflected in the column. We will mask the column pins and it is read to a variable. The column value is checked against a switch case to identify the pressed key. The switch case value 0XE0 matches in that case.

A similar procedure is followed for the rest of the rows. The While statement waits till the key pressed state changes and avoids denouncing and also we can add a small delay to ensure a proper reading. We can show the detected keypress in any of the display modules according to your convenience. We have to write a logic high to row pins one by one and we will scan the column pins to detect the keypress. The below code is the example using the above functions.

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Exclusive Content for members only.Keypads are small keyboards that are used to enter numeric, alphanumeric or select configuration data to microcontroller systems. Keypads are available in a variety of sizes. Keypads are widely used input devices with lots of application in our everyday life, devices like telephone, ATM, electronic lock, Calculator, timers just to name a few, all have some sort of a keypad.

A matrix keypad is basically a combination of push-buttons in a way to form rows and columns. In the matrix keypad switches are connected in a special manner as shown in figure 2 below. The values of each key could be mapped according to ones specific project application.

D etecting a pressed Key. Assuming that the keypad is connected to PORTB as shown on figure 5, the steps to determine which key is pressed are as follows:. Below is a quick descriptions of the Keypad library, for more information, please visit online the mikroC pro for PIC Keypad Library page.

The global variable keypadPort must be defined first before using this function.

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This function reads the key from keypad when key gets pressed. The code of a pressed key If no key is pressed, returns 0. The keypad has to be initialized first before calling this function. This function waits until some key is pressed and released this is a blocking call. If more than one key is pressed simultaneously the function will wait until all pressed keys are released.

After that the function will return the code of the first pressed key. This is a simple example of using the Keypad Library. It can support keypads with You can download the full project files MikroC source code and Proteus Schematic design below here. All the files are zipped, you will need to unzip them Download a free version of the Winzip utility to unzip files. Proteus Schematic: Keypad Proteus Schematic design.

Bitahwa Bindu.The LED shown in the schematic is just extra, which can be used anyway you like. Here, the mega32 reads the code of key pressed and sends relevant character to display on LCD 2nd line.

Project 17 – Interface with 4×4 keypad and 2×16 LCD

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4x4 matrix keypad c code for pic16f877a

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Interfacing 4x4 Matrix KeyPad with PIC16F877A PROBLEM

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Interfacing LCD and Keypad with PIC16F877A Microcontroller

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A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. Here we are using 4 X 4 matrix keypad. The rows are connected to an output port and the columns are connected to an input port. To detect a pressed key, the microcontroller grounds all rows by providing 0 to the output latch, and then it reads the columns.

However, if one of the column bits has a zero, this means that a key press has occurred. After a key press is detected, the microcontroller will go through the process of identifying the key. Starting with the top row, the microcontroller grounds it by providing a low to row D0 only; then it reads the columns. If the data read is all 1s, no key in that row is activated and the process is moved to the next row.

It grounds the next row, reads the columns, and checks for any zero. This process continues until the row is identified. After identification of the row in which the key has been pressed, the next task is to find out which column the pressed key belongs to. In case of 4X4 matrix Keypad both the ends of switches are connected to the port pin i. So in all sixteen switches have been interfaced using just eight lines.

The Interfacing keypad with PIC16FA program is very simple and straight forward, that scan a keypad rows and columns. They must be properly set up and a project with correct settings must be created in order to compile the code. To compile the above code, the C file must be added to the project. In Mplab, you want to develop or debug the project without any hardware setup.

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You must compile the code for generating HEX file. Open the Hyper Terminal screen, select which port you are using and set the default settings. And also check the keypad keys are properly working or not.

Otherwise you just check the code with debugging mode in Mplab. Wherever possible use new components.

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