Embedded Applications - Wavecom GR64 GSM/GPRS Integrator's Manual

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CAUTION
If pins labelled in the table above are not being used for the indicated alternative
function they may be used as general purpose inputs or outputs; they are not
constrained to work in only one direction. All GPIO is level shifted on the GR64, and
has the characteristics defined in section 5.3.
GPIO has a number of sharing (configuration) options. Sharing means that it is not
feasible to operate all the alternative features concurrently, however, with care,
dynamic switching from one feature to another is possible.
Users should note that if flow control is required for UART1 then GPIOs 7 to 12
inclusive cannot be configured for general purpose use.
Some GPIO is configured to provide a keyboard interface (details are covered in the
next section).

5.16.1 Embedded Applications

When a particular IO feature is required, the user sets the state of the relevant IO
blocks by disabling one set before enabling others.
The Wireless CPU checks the state of the IO when the user requests a new function.
The new function is rejected if the current function is not released first.
The states of GPIOn to GPIOm are retained for the next power up.
inputs remain as inputs and outputs remain as outputs. The voltage of a defined
output pin will still drop to 0 Volts in the Wireless CPU power down state.
GR64 Integrators Manual
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Open drain or direct drive
Polarity (inversion)
Internal pull-up resistors
The internal pull-up resistors are applied on the Wireless CPU side of
the level translators. If the application is using a GPIO as an input and
need a pull-up resistor, the application must provide that externally.
To overcome the 6k input impedance of the level translator, the pull-
up resistor must be in the 680 ohm range. This could potentially
increase current consumption, so it is recommended to use CMOS-
logic (see 5.3.1.1 for more information).
It is recommended to use the GPIO's as direct drive with internal pull-
up resistors disabled.
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