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]

O

8-bit matrix-scan outputs

P1[7:0]

O

8-bit matrix-scan outputs

P3.6

O

1-bit matrix-scan output

P3.7

O

1-bit matrix-scan output

P2[7:0]

I

8-bit matrix-scan inputs

P3.2

O

Keyboard LED-1

P3.3

O

Keyboard LED-2

P3.4

O

Keyboard LED-3

P3.5

O

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