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ADP5585ACPZ-00-R7 Datasheet(PDF) 11 Page - Analog Devices |
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ADP5585ACPZ-00-R7 Datasheet(HTML) 11 Page - Analog Devices |
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11 / 40 page  Data Sheet ADP5585 Rev. C | Page 11 of 40 Use Registers PIN_CONFIG_A[7:0] and PIN_CONFIG_B[7:0] to configure I/Os for keypad decoding. The number label on each key switch represents the event identifier that is recorded if that switch was pressed. If all row/column pins are config- ured, it is possible to observe all 25 key identifiers on the FIFO. A larger 6 × 5 matrix can be configured by using the ADP5585ACBZ-01-R7 or the ADP5585ACPZ-01-R7. If a smaller 2 × 2 matrix is configured, for example, by using the C2 and C3 column pins and the R1 and R2 row pins, only the four event identifiers (8, 9, 13, and 14) can possibly be observed on the FIFO, as shown in Figure 11. By default, ADP5585 records key presses and releases on the FIFO. Figure 12 illustrates what happens when a single key is pressed and released. Initially, the key scanner is idle. When Key 3 is pressed, the scanner begins scanning through all configured row/column pairs. After the scan wait time, the scanner again scans through all configured row/column pairs and detects that Key 3 has remained pressed, which sets the EVENT_INT interrupt. The event counter, EC[4:0], is incre- mented to 1, EVENT1_IDENTIFIER[6:0] of the FIFO is updated with its event identifier set to 3, and its EVENT1_STATE bit is set to 1, indicating a press. KEY 3 KEY 3 PRESS KEY 3 RELEASE KEY SCAN EVENT_INT EC[4:0] FIFO 1 2 1 0 0 0 3 3 0 0 Figure 12. Press and Release Event The key scanner continues the scan/wait cycles while the key remains pressed. If the scanner detects that the key has been released for two consecutive scan cycles, the event counter, EC[4:0], is incremented to 2, and EVENT2_IDENTIFIER[6:0] of the FIFO is updated with its event identifier set to 3. Its EVENT2_STATE bit is set to 0, indicating a release. The key scanner returns to idle mode because no other keys are pressed. The EVENT_INT interrupt can be triggered by both press and release key events. As shown in Figure 14, if Key 3 is pressed, EVENT_INT is asserted, EC[4:0] is updated, and the FIFO is updated. During the time that the key remains pressed, it is possible for the FIFO to be read, the event counter decremented to 0, and EVENT_INT cleared. When the key is finally released, EVENT_INT is asserted, the event counter is incremented, and the FIFO is updated with the release event information. KEY 3 KEY 3 PRESS KEY 32 RELEASE KEY SCAN EVENT_INT EVENT_INT CLEARED EC[4:0] FIFO FIFO READ 0 0 0 0 0 0 0 0 FIFO 1 0 0 0 3 0 0 0 FIFO 10 1 0 0 0 0 3 0 0 0 Figure 13. Asserting the EVENT_INT Interrupt Key Pad Extension As shown in Figure 11, the keypad can be extended if each row is connected directly to ground by a switch. If the switch placed between R0 and ground is pressed, the entire row is grounded. When the key scanner completes scanning, it normally detects Key 1 to Key 5 as being pressed; however, this unique condition is decoded by the ADP5585, and Key Event 31 is assigned to it. Up to eight more key event assignments are possible, allowing the keypad size to extend up to 30. However, if one of the extended keys is pressed, none of the keys on that row is detectable. Activation of a ground key causes all other keys sharing that row to be undetectable. Ghosting Ghosting is an occurrence where, given certain key press com- binations on a keypad matrix, a false positive reading of an additional key is detected. Ghosting is created when three or more keys are pressed simultaneously on multiple rows or columns (see Figure 14). Key combinations that form a right angle on the keypad matrix can cause ghosting. The solution to ghosting is to select a keypad matrix layout that takes into account three key combinations that are most likely to be pressed together. Multiple keys pressed across one row or across one column do not cause ghosting. Staggering keys so that they do not share a column also avoids ghosting. The most common practice is to place keys that are likely to be pressed together in the same row or column. Some examples of keys that are likely to be pressed together are as follows: The navigation keys in combination with Select. The navigation keys in combination with the space bar. The reset combination keys, such as CTRL + ALT + DEL. COL0 ROW0 ROW1 ROW2 ROW3 PRESS GHOST PRESS PRESS COL1 COL2 Figure 14. COL0: ROW3 is a Ghost Key Due to a Short Among ROW0, COL0, COL2, and ROW3 During Key Press |
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