User's Manual

GC864 Hardware User Guide

1vv0300733 Rev. 0 - 12/06/06

10 General Purpose I/O

The general purpose I/O pads can be configured to act in three different ways:

- input

- output

- alternate function (internally controlled)

Input pads can only be read and report the digital value (high or low) present on the pad at the read

time; output pads can only be written or queried and set the value of the pad output; an alternate

function pad is internally controlled by the GC864 firmware and acts depending on the function

implemented.

Not all GPIO pads support all these three modes:

- GPIO_06/ALARM supports all three modes and can be input, output, alarm output (Alternate

function)

- GPIO_07/BUZZER supports all three modes and can be input, output, buzzer output (Alternate

function)

10.1 Using a GPIO pad as INPUT

The GPIO pads, when used as inputs, can be connected to a digital output of another device and

report its status, provided this device has interface levels compatible with the 2.8V CMOS levels of the

GPIO.

If the digital output of the device to be connected with the GPIO input pad has interface levels different

from the 2.8V CMOS, then it can be connected to GPIO1 or can be buffered with an open collector

transistor, provided a 47KΩ pull-up resistor is connected as seen in the paragraph 6.2

5V UART Level translation.

10.2 Using a GPIO pad as OUTPUT

The GPIO pads, when used as outputs, can drive 2.8V CMOS digital devices or compatible hardware.

When set as outputs, the pads have a push-pull output and therefore the pull-up resistor may be

omitted.