TUSB3410 datasheet(59/92 Pages) TI

59 / 92 page

8–1

8 Expanded GPIO Port

8.1

Input/Output and Control Registers

The TUSB3410 has four general-purpose I/O pins (P3.0, P3.1, P3.3, P3.4) that are controlled by firmware running

on the MCU. Each pin can be controlled individually and each is implemented with a 12-mA push/pull Cmos output

with tristate control plus input. The MCU treats the outputs as open drain types in that the output can be driven low

continuously, but a high output is driven for two clock cycles and then the output is tristated.

An input pin can be read using the MOV instruction. For example, MOV C,P3.3 reads the input on P3.3. As a

precaution, be certain the associated output is tristated before reading the input.

An output can be set high (and then tristated) using the SETB instruction. For example, SETB P3.1 sets P3.1 high.

An output can be set low using the CLR instruction, as in CLR P3.4, which sets P3.4 low (driven continuously until

changed).

Each GPIO pin has an associated internal pullup resistor. It is strongly recommended that the pullup resistor remain

connected to the pin to prevent oscillations in the input buffer. The only exception is if an external source always drives

the input.

8.1.1

PUR_3: GPIO Pullup Register For Port 3 (Addr:FF9E)

765

RSV

Pin3

RSV

Pin1

Pin0

R/O

R/W

R/O

R/W

BIT

NAME

RESET

FUNCTION

0–7

Pin N

(N = 0 to 7)

The MCU may write to this register. If the MCU sets this bit to 1, the pullup resistor is disconnected from

the pin. If the MCU clears this bit to 0, the pullup resistor is connected to the pin. The pullup resistor is

connected to the VCC power supply.

TUSB3410 Datasheet(PDF) 59 Page - Texas Instruments