UM0851 datasheet(179/245 Pages) STMICROELECTRONICS

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UM0851

Human interface device (HID) drivers

Doc ID 16604 Rev 2

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Control Register bits b3 and b2 determine the keypad scanning rate. Each time the timer

count expires, the keypad is scanned. If only one key down is detected and it is the same

key as in the previous scan, a bit is set in the Status register indicating New Key Data. The

code for the key is written to the keyboard value register. Key release is signaled only once.

The keypad encoder initialization is made once only when the application starts (setting the

prescaler load value, keypad enable, scan rate, keypad operation mode). The software then

handles the keypad interrupts.

The following table shows the assignment of the keypad matrix signals on the SPEAr300

PL_GPIO pins.

7.2.2

Software overview

The keypad is a 18-pin interface module that is used to detect the pressed key in an 9x9

(maximum) keypad matrix. The size of the input keypad matrix is software programmable.

The keypad module supports two modes of operation, press-release-press mode and press-

hold mode. Press-release-press mode identifies a press-release-press sequence of a key

as two consecutive presses of the same key. Press-hold mode checks the input key's state

at periodic intervals to determine the number of times the same key has been pressed.

Table 47.

PL GPIO keypad pins

Port Pin

PL_GPIO

Keypad

ROW0

PL_GPIO87

output kbd(row)0

ROW1

PL_GPIO86

output kbd(row)1

ROW2

PL_GPIO85

output kbd(row)2

ROW3

PL_GPIO84

output kbd(row)3

ROW4

PL_GPIO83

output kbd(row)4

ROW5

PL_GPIO82

output kbd(row)5

ROW6

PL_GPIO81

output kbd(row)6

ROW7

PL_GPIO56

output kbd(row)7

ROW8

PL_GPIO55

output kbd(row)8

COLUMN0

PL_GPIO96

Input kbd(column)0

COLUMN1

PL_GPIO95

Input kbd(column)1

COLUMN2

PL_GPIO94

Input kbd(column)2

COLUMN3

PL_GPIO93

Input kbd(column)3

COLUMN4

PL_GPIO92

Input kbd(column)4

COLUMN5

PL_GPIO91

Input kbd(column)5

COLUMN6

PL_GPIO90

Input kbd(column)6

COLUMN7

PL_GPIO89

Input kbd(column)7

COLUMN8

PL_GPIO88

Input kbd(column)8

UM0851 Datasheet(PDF) 179 Page - STMicroelectronics

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