ADP5586ACBZ-00-R7 datasheet(10/44 Pages) AD

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ADP5586

Data Sheet

Rev. 0 | Page 10 of 44

KEY SCAN CONTROL

General

The 10 input/output pins can be configured to decode a keypad

matrix up to a maximum size of 25 switches (5 × 5 matrix) using

the PIN_CONFIG_A, PIN_CONFIG_B, and PIN_CONFIG_C

registers (Registers 0x3A through 0x3C). Smaller matrices can

also be configured, making the unused row and column pins

available for other I/O functions.

The R0 through R4 I/O pins comprise the rows of the keypad

matrix. The C0 through C4 I/O pins comprise the columns of

the keypad matrix. Pins that are used as rows are pulled up via the

internal 300 kΩ (or 100 kΩ) resistors. Pins that are used as

columns are driven low via the internal NMOS current sink.

3 × 3 KEYPAD MATRIX

KEY

SCAN

CONTROL

VDD

Figure 8. Simplified Key Scan Block

Figure 8 shows a simplified representation of the key scan block

using three row pins 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 has been pulled low,

and a key scan cycle begins. Key scanning involves driving all

column pins high, then driving each column pin low, one at a

time, and sensing whether a row pin is low. All row/column pairs

are scanned; therefore, if multiple keys are pressed, they are

detected.

To prevent a glitch or narrow press time from being registered

as a valid key press, the key scanner requires that 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 and

wait for as long as the key is pressed.

If Switch 6 is released, the connection between R1 and C2 breaks,

and R1 is pulled 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. Up to two full wait/scan

cycles may be required for a key to register as released. When

the key registers as released, and no other keys are pressed, the key

scanner returns to idle mode.

For the remainder of this data sheet, 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

level represents released. This eliminates the need to draw

individual row/column signals when describing key events.

KEY x

KEY RELEASED

KEY PRESSED

Figure 9. Logic Low: Key Released; Logic High: Key Pressed

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