TUSB2136 datasheet(46/53 Pages) TI

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4−1

4 Application

4.1

Keyboard Section

Table 4−1 outlines the GPIO assignment for the switch-matrix scanning and for keyboard LED drive. Figure 4−1

illustrates the port-3 pins that are assigned to drive the four keyboard LEDs. As shown, P3[5:2] can sink up to 12 mA

(open-drain output) on each pin. Figure 4−2 illustrates the 18 outputs (open-drain) and the 8 inputs (internal pullups)

that are used for the switch-matrix scanning. Figure 4−3 illustrates the partial connection bus power mode. Figure

4−4 shows the USB upstream connection, and Figure 4−5 illustrates the downstream connection (only one port

shown).

Table 4−1. GPIO Assignment for Matrix Scan and LED Drive

GPIO

I/O

P0[7:0]

8-bit matrix-scan outputs

P1[7:0]

8-bit matrix-scan outputs

P3.6

1-bit matrix-scan output

P3.7

1-bit matrix-scan output

P2[7:0]

8-bit matrix-scan inputs

P3.2

Keyboard LED-1

P3.3

Keyboard LED-2

P3.4

Keyboard LED-3

P3.5

Keyboard LED-4

P3.0

I/O

GPIO (Not used for keyboard)

P3.1

I/O

GPIO (Not used for keyboard)

TUSB2136

P3.2

P3.3

P3.4

P3.5

VCC

Figure 4−1. Keyboard LED Connection

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