• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 98 subscribers
  • Views 401 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OMAPL138 - Unused RTC-Alarm Pin Termination

Michael Questo
Expert 6000 points
Other Parts Discussed in Thread: OMAPL138

OMAPL138 Champs,

I am trying to determine how to best terminate my unused RTC_ALARM/UART2_CTS/GP0[8]/DEEPSLEEP ball F4 on the OMAPL138

According to section 1.5.10 Pin Multiplexing Control Registers (PINMUX0-PINMUX19) of the technical reference manual (TRM) the default state of this ball (i.e. PINMUX0 = 0x0) will be DEEPSLEEP which is an input.  It is also part of CP[0] which will default to an internal pull up according to 11.5.23 Pullup/Pulldown Select Register (PUPD_SEL) in the TRM.

The Schematic checklist and the Section 2.9 Unused Pin Configurations in the Data Sheet only state the following. "RTC_ALARM May be used as GPIO or other peripheral function"  This is fairly unclear.

My questions:
1. Since this ball defaults to an input, will I need to use an external IPU in order to avoid a floating input in the case that the device is held in reset? 
2. Similarly in order to avoid a floating input during runtime is it recommend to set this ball to an output such that the IPU will take effect?
 
Useful Links:

Thanks!

  • 0
    TI__Expert 6000 points

    There is a recommended opposing and complimenting values in Section 3.3 Pullup/Pulldown Resistors in the Datasheet. 

    Opposing - A 1-kohm resistor can be used to oppose the IPU/IPD while meeting the above criteria.
    Complimenting - A 20-kohm resistor can be used to compliment the IPU/IPD on the boot and configuration pins while meeting the above criteria.

     Most pins will by default come up as High Z, in case they do not there are two options.

    1.  If the Pin is by default an input. 

    - Check the IPU/IPD state of each pin is determined by the PUPD_ENA and PUPD_SEL registers.  These registers have default states which are listed in 11.5.22 Pullup/Pulldown Enable Register and 11.5.23 Pullup/Pulldown Select Register in the TRM.  You can determine which IPU or IPD effects each pin by cross-referencing the functional groups (CP[n])  to the pin using the table found in Section 2.8 Terminal Functions.  By default all IPU/IPD will be enabled and all but functional groups CP[26-29] will be set to pull-ups.

    2. If the Pin is by default an output

    - This only occurs in the default state for RESETOUT/UHPI_HAS/PRU1_R30[14]/GP6[15] and RTCK/GP8[0] Control referencing.  Both RESETOUT and RTCK are specific functional pins and care should be taken to terminate them accordlingly if they are not used.  Please see their particular sections in the TRM in order to understand their I/O state is not opposed.  If you choose to switch either of these or any other pin to a GPIO output then they will be driven to either a logic high or low, this register is described in 21.3.4 GPIO Output Data Registers.  By default they will all be logic 0 unless otherwised changed.

  • 0 in reply to Michael Questo
    TI__Expert 7470 points

    Michael,

    My answer below:

    Michael Questo said:
    1. Since this ball defaults to an input, will I need to use an external IPU in order to avoid a floating input in the case that the device is held in reset?

    Once the reset is released, the IPD/IPU take effect. But for the duration that reset is asserted, the status of the Pullup/Pulldown Enable Register (PUPD_ENA) is not deterministic. If customer expects that the device will be held in reset for longer than the required duration, an external IPU can be used to prevent a floating input.

    Michael Questo said:
    2. Similarly in order to avoid a floating input during runtime is it recommend to set this ball to an output such that the IPU will take effect?

    Not required, since as long as the Pullup/Pulldown Enable Register is correctly setup, IPD/IPU will take effect for input or output pins.

    Regards,

    Sunil Kamath