PC87393F datasheet(73/148 Pages) NSC

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3.0 General-Purpose Input/Output (GPIO) Port (Continued)

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3.2

BASIC FUNCTIONALITY

The basic functionality of each GPIO pin is based on four configuration bits and a bit slice of runtime registers GPDO and

GPDI. The configuration and operation of a single pin GPIOXn (pin n in port X) is shown in Figure 9.

Figure 9. GPIO Basic Functionality

3.2.1

Configuration Options

The GPCFG register controls the following basic configuration options:

• Port Direction - Controlled by the Output Enable bit (bit 0)

• Output Type - Push-pull vs. open-drain. It is controlled by Output Buffer Type (bit 1) by enabling/disabling the pull-up

portion of the output buffer.

• Weak Static Pull-Up - May be added to any type of port (input, open-drain or push-pull). It is controlled by Pull-Up Control

(bit 2).

• Pin Lock - GPIO pin may be locked to prevent any changes in the output value and/or the output characteristics. The

lock is controlled by Lock (bit 3). It disables writes to the GPDO register bits, and to bits 0-3 of the GPCFG register (In-

cluding the Lock bit itself). Once locked, it can be released by hardware reset only.

3.2.2

Operation

The value that is written to the GPDO register is driven to the pin, if the output is enabled. Reading from the GPDO register

returns its contents, regardless of the pin value or the port configuration. The GPDI register is a read-only register. Reading

from the GPDI register returns the pin value, regardless of what is driving it (the port itself, configured as an output port, or

the external device when the port is configured as an input port). Writing to this register is ignored.

Activation of the GPIO port is controlled by external device specific configuration bit (or a combination of bits). When the port

is inactive, access to GPDI and GPDO registers is disabled, and the inputs are blocked. However, there is no change in the

port configuration and in the GPDO value, and hence there is no effect on the outputs of the pins.

GPIO Device

Data Out

Data In

Enable

Output

Enable

Output

Internal

Bus

Lock

Type

Static

Pull-Up

Enable

GPIO Pin Conﬁguration (GPCFG) Register

Push-Pull =1

Pull-Up

Control

Read Only

Read/Write

Bit 3

Bit 2

Bit 1

Bit 0

PC87393F Datasheet(PDF) 73 Page - National Semiconductor (TI)

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