Wavecom GR64 Application Note - page 5
2
GPIO vs. Alternate I/O Functions
Many of the GPIO pins can be configured to perform dedicated operations such as
activity indication, modem control, SD/MMC memory support or I
2
C. These dedicated
operations are known as alternate I/O functions. While the number of GPIO and
dedicated tasks that can be active simultaneously is limited by this technique, the
Wireless CPU size, power consumption and pin count are kept small with no decrease
in flexibility to meet application requirements.
•
Section 3 describes how to use and control GPIO pins.
•
Section 4 describes available alternate I/O functions.
2.1 Default Settings
The factory default setting of all IO’s is as input signals and pulled up. If a signal is
changed by the application and stored with AT&W the change is stored so that the
next time the Wireless CPU is powered up the IO will maintain the new customer
setting.
2.2 At*GPIO or Alternate Function Selection
The integrator should understand that the use of a pin for GPIO or an alternate
function is exclusive. If an attempt is made to issue GPIO commands on a pin that is
enabled for an alternate I/O function, the GPIO command will return an error
indication. When the alternate function has been disabled, GPIO commands may once
again be issued without error on the pin.
Please consult the table in Appendix A for the GR/GS64 Wireless CPU type that is
used. Each table describes the pins available for GPIO use and indicates if a pin is
part of an alternate function. Select pins for GPIO that do not belong to an alternate
function that is also needed.
For example, suppose that two GPIO pins are needed in a GR64 application, one to
monitor a contact closure and another to control a relay. The application must also
minimize power consumption, so the GR64 will be placed in standby mode
periodically. Standby mode requires the use of the modem control lines which are an
alternate function of the GPIO7-GPIO12 pins. Therefore, do not select the monitor
and control pins from the GPIO7-GPIO12 group. In this example, we select GPIO1 to
monitor the contact closure and GPIO2 to control the relay.
APPLICATION NOTE
GR/GS64 General Purpose and
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Alternate Function I/O
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