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ADP5589ACBZ-02-R7 Datasheet(PDF) 10 Page - Analog Devices |
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ADP5589ACBZ-02-R7 Datasheet(HTML) 10 Page - Analog Devices |
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10 / 52 page  ADP5589 Data Sheet Rev. B | Page 10 of 52 KEY SCAN CONTROL 1 2 3 4 5 6 7 8 9 VDD R0 R1 R2 C2 C0 C1 3 × 3 KEYPAD MATRIX Figure 9. Simplified Key Scan Block Figure 9 shows a simplified representation of the key scan block using three row and three column pins connected to a small 3 × 3, nine-switch keypad matrix. When the key scanner is idle, the row pins are pulled high and the column pins are driven low. The key scanner operates by checking the row pins to see if they are low. If Switch 6 in the matrix is pressed, R1 connects to C2. The key scan circuit senses that one of the row pins is pulled low, and a key scan cycle begins. Key scanning involves driving all column pins high, then driving each column pin, one at a time, low and sensing whether a row pin is low or not. All row/column pairs are scanned; therefore, if multiple keys are pressed, they are detected. To prevent glitches or narrow press times being registered as a valid key press, the key scanner requires the key be pressed for two scan cycles. The key scanner has a wait time between each scan cycle; therefore, the key must be pressed and held for at least this wait time to register as being pressed. If the key is continuously pressed, the key scanner continues to scan, wait, scan, wait, and so forth. If Switch 6 is released, the connection between R1 and C2 breaks, and R1 is pulled up high. The key scanner requires that the key be released for two scan cycles because the release of a key is not necessarily in sync with the key scanner, it may take up to two full wait/scan cycles for a key to register as released. When the key is registered as released, and no other keys are pressed, the key scanner returns to idle mode. For the remainder of this document, the press/release status of a key is represented as simply a logic signal in the figures. A logic high level represents the key status as pressed, and a logic low represents released. This eliminates the need to draw individual row/column signals when describing key events. KEY x KEY RELEASED KEY RELEASED KEY PRESSED Figure 10. Logic Low: Released; Logic High: Pressed Figure 11 shows a detailed representation of the key scan block and its associated control and status signals. When all row and column pins are used, a matrix of 88 unique keys can be scanned. |
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