In a matrix keypad, row and column lines are connected to the two terminals of each key switch. The row lines are pulled up to +5V via pull-up resistors. When no key is pressed, the row lines remain at a high logic level. When a key is pressed, the corresponding row and column lines are connected, causing the voltage level of that row line to be determined by the voltage level of the connected column line. This behavior is fundamental to detecting whether a key in the matrix has been pressed. However, since multiple keys share the same row and column lines, pressing any key affects the electrical state of its entire row and column, creating mutual interference among keys. Therefore, coordinated processing of both row and column lines is required to accurately identify the exact position of the pressed key.

Scanning Method

      When a key is pressed, the row and column lines connected to it become conductive. Since row lines sit at a high level when idle, setting all column lines to a high level as well would prevent any detectable voltage change on the row lines when a key is pressed. Consequently, all column lines must initially be set to a low level. Only under this condition will pressing a key pull the corresponding row line from high to low, allowing the CPU to determine which row contains an active key based on this voltage transition.

      For example, if Key #8 is pressed, Row 2 will read low. However, a low reading on Row 2 does not definitively indicate Key #8, as Keys #9, #10, or #11 would produce the identical signal. To pinpoint the exact key, all column lines cannot be held low simultaneously. Instead, only one column line is driven low at a time while all others remain high; then the next column is driven low in sequence, cycling through continuously. This sequential method of activating one column at a time is known as keyboard scanning.

About Yuyao Xianglong Communication Industrial Co., Ltd.

      Yuyao Xianglong Communication Industrial Co., Ltd. is a professional manufacturer of industrial telephone accessories and specialized keypads. Our product portfolio includes:

Industrial digital keypads

Access control keypads

Fuel dispenser keypads

Vending machine keypads

Banking numeric keypads

Self-service terminal keypads

Medical-grade keypads

Coal mine telephone handsets

Smart terminal telephone handsets

All products feature waterproof, dustproof, vandal-proof, and anti-static designs for demanding environments.

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