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Original question:

TM4C1294NCPDT: PTP PPS question

TM4C1294NCPDT: EN0PPS output on TM4C1294

Richard Schrader
Prodigy 75 points

Part Number: TM4C1294NCPDT
Other Parts Discussed in Thread: EK-TM4C1294XL

Tool/software:

I'm using the EK-TM4C1294XL running a PTP (IEEE1588) slave clock to generate PPS signal on PG0 and comparing it with the PPS output from other two GNSS receivers from TRIMBLE and UBLOX.

Here how I'm initializing the EN0PPS:

MAP_GPIOPadConfigSet(GPIO_PORTG_BASE, GPIO_PIN_0, GPIO_STRENGTH_12MA, GPIO_PIN_TYPE_STD);

MAP_GPIODirModeSet(GPIO_PORTG_BASE, GPIO_PIN_0, GPIO_DIR_MODE_HW);

MAP_GPIOPinConfigure(GPIO_PG0_EN0PPS); 

On my oscilloscope display, the falling edge of EN0PPS matches the rising edge of the other two GNSS receivers, but I can't understand or find any documentation explaining this.

I checked the GNSS receivers, and both have a PPS rising edge of TOS, which means the PPS rising edge matches exactly (too strong word) the beginning of the second.

Can someone please help me understand why the EN0PPS output is generating a falling edge on the beginning of the second?

Channel 1 on top is the EN0PPS and the other two the GNSS receivers PPS output.

 
Thanks,

Richard

  • 0
    TI__Guru**** 191886 points

    HI,

    Richard Schrader said:

    MAP_GPIOPadConfigSet(GPIO_PORTG_BASE, GPIO_PIN_0, GPIO_STRENGTH_12MA, GPIO_PIN_TYPE_STD);

    MAP_GPIODirModeSet(GPIO_PORTG_BASE, GPIO_PIN_0, GPIO_DIR_MODE_HW);

    MAP_GPIOPinConfigure(GPIO_PG0_EN0PPS); 

    As far as the PG0 pin configuration, I don't see a problem here. 

    Richard Schrader said:
    On my oscilloscope display, the falling edge of EN0PPS matches the rising edge of the other two GNSS receivers, but I can't understand or find any documentation explaining this. I checked the GNSS receivers, and both have a PPS rising edge of TOS, which means the PPS rising edge matches exactly (too strong word) the beginning of the second. Can someone please help me understand why the EN0PPS output is generating a falling edge on the beginning of the second?

    Channel 1 on top is the EN0PPS and the other two the GNSS receivers PPS output.

    Looking at your scope cap, it seems that the scale is 500ns per division. Is that correct? if this is the case, the rise edge of EN0PPS is 7 divisions or 3.5us ahead of the other two rise edges. I'm not sure if you are using the Fix PPS Output or the Flexible PPS. Reading the datasheet, you can define the start or stop time and the signal internal width and interval among others. I will suggest you play with these parameters to see if you can get them lined up more closely with the other two PPS. Personally, I have no experience with the PPS mode.