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GM862-GPS Hardware User Guide
1vv0300728 Rev. 0 - 27/04/06
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 45 of 55
7 General Purpose I/O
The general purpose I/O pins can be configured to act in three different ways:
- input
- output
- alternate function (internally controlled)
Input pins can only be read and report the digital value (high or low) present on the pin at the read
time; output pins can only be written or queried and set the value of the pin output; an alternate
function pin is internally controlled by the GM862-GPS firmware and acts depending on the function
implemented.
Not all GPIO pins support all these three modes:
- GPIO1 is an INPUT ONLY
- GPIO2 is an OUTPUT ONLY (open collector)
- GPIO3, GPIO4 and GPIO5 support both input or output mode but not Alternate function.
- GPIO6 supports all three modes and can be input, output, alarm output (Alternate function)
- GPIO7 supports all three modes and can be input, output, buzzer output (Alternate function)
All GPIO pins except from GPIO1 and GPIO2 that are buffered with a transistor, are 2.8V CMOS
signals and their interface levels are the same specified in the paragraph 4 Serial Port.
7.1 Using a GPIO pin as INPUT
The GPIO pins, 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 pin 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 4.2 5V UART level
translation.
7.2 Using a GPIO pin as OUTPUT
The GPIO pins, when used as outputs, can drive 2.8V CMOS digital devices or compatible hardware.
When set as outputs, the pins (except from GPIO2 which is Open Collector) have a push-pull output
and therefore the pull-up resistor may be omitted.
The GPIO2 pin, since it is an Open Collector output needs an external pull-up resistor.