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Before learning “Interfacing Matrix Keypad to Microcontroller” you should know how to interface a switch to microcontroller for which please click here. |
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As you have seen in the article for interfacing switches to microcontroller normally the port pin is high but when a switch is pressed the controller pin gets a Low signal and we come to know that a switch has been pressed. One end of switch is connected to the port pin whereas the other end is connected to the Ground. |
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In case of matrix Keypad both the ends of switches are connected to the port Pin. Over here we have considered a 4x3 matrix keypad i.e. four rows and three columns. So in all twelve switches have been interfaced using just seven lines. |
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The adjoining figure shows the diagram of a matrix keypad and how it is interfaced with the controller. |
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As you can see no pin is connected to ground, over here the controller pin itself provides the ground. We pull one of the Column Pins low & check the row pins if any of the Pin is low then we come to know which switch is pressed. |
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Suppose we make column 1 pin low and while checking the rows we get Row 3 is low then we come to know switch 7 has been pressed. |
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ALGORITHM |
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1. Start. |
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2. Make All Pins High. |
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3. Make Column 1 pin low. |
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4. Check if Row 1 is low, if yes then Switch 1 has been pressed. |
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5. Check if Row 2 is low, if yes then Switch 4 has been pressed. |
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6. Check if row 3 is low if yes then Switch 7 has been pressed. |
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7. Check if row 4 is low if yes then Switch 10 has been pressed. |
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8. Make Column 1 Pin high & Column 2 Pin Low. |
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9. Check if Row 1 is low, if yes then Switch 2 has been pressed. |
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10. Check if Row 2 is low, if yes then Switch 5 has been pressed. |
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11. Check if row 3 is low if yes then Switch 8 has been pressed. |
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12. Check if row 4 is low if yes then Switch 11 has been pressed. |
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13. Make Column 2 Pin high & Column 3 Pin Low. |
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14. Check if Row 1 is low, if yes then Switch 3 has been pressed. |
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15. Check if Row 2 is low, if yes then Switch 6 has been pressed. |
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16. Check if row 3 is low if yes then Switch 9 has been pressed. |
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17. Check if row 4 is low if yes then Switch 12 has been pressed. |
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18. Make column 3 pin high. |
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19. Stop. |
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Please make sure at any time only one column Pin should remain Low. |
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For the complete working code in Assembly please check the code library or click here. |
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