Keyboard Scanning Sequence; Mpuio Keyboard Interface - Texas Instruments OMAP5910 Technical Reference Manual

Hide thumbs Also See for OMAP5910:

Table of Contents

Table 7-11. Keyboard Scanning Sequence

To allow button press detection:

All the row lines (KB.R) must have an external pullup.

All the column lines (KB.C) drive a low level (idle state of Table 7-11).

The output drivers of the KBC output pins act as open-drain outputs in that

they only drive low or are 3-state. So external pullup resistors are required

to achieve a high state when these outputs are 3-stated.

The keyboard interrupt (keyboard_int) to the MPU is an AND of the eight row

lines filtering during one 32-kHz clock period (CLK_32KHZ).

As soon as any key of the keyboard matrix is pressed, the corresponding row

and column lines are shorted together and a low level is driven on the

corresponding row line, generating a keyboard interrupt (see Figure 7-11).

Once the keyboard interrupt is received, the MPU scans the column lines in

the sequence described in the Table 7-11 in order to detect the key that has

been pressed.

For each step of the sequence, the MPU:

Writes the specific value (with a low level on one column line) in the

KBC_REG register

Reads the value of the KBR_LATCH register and thus detects if one key

of the concerned column line (this one which drives a low level) is pressed

At the end of the scanning sequence, the MPU is able to establish which keys

have been pressed.

Keyboard Scanning

MPU Public Peripherals