SPRZ423K October   2014  – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076

 

  1.   1
  2.   Abstract
  3. 1Usage Notes and Advisories Matrices
    1. 1.1 Usage Notes Matrix
    2. 1.2 Advisories Matrix
  4. 2Nomenclature, Package Symbolization, and Revision Identification
    1. 2.1 Device and Development Support Tool Nomenclature
    2. 2.2 Devices Supported
    3. 2.3 Package Symbolization and Revision Identification
  5. 3Silicon Revision C Usage Notes and Advisories
    1. 3.1 Silicon Revision C Usage Notes
      1. 3.1.1 PIE: Spurious Nested Interrupt After Back-to-Back PIEACK Write and Manual CPU Interrupt Mask Clear
      2. 3.1.2 Caution While Using Nested Interrupts
      3. 3.1.3 SYS/BIOS: Version Implemented in Device ROM is not Maintained
      4. 3.1.4 SDFM: Use Caution While Using SDFM Under Noisy Conditions
      5. 3.1.5 McBSP: XRDY Bit can Hold the Not-Ready Status (0) if New Data is Written to the DX1 Register Without Verifying if the XRDY Bit is in its Ready State (1)
    2. 3.2 Silicon Revision C Advisories
      1.      Advisory
      2.      Advisory
      3.      Advisory
      4.      Advisory
      5.      Advisory
      6.      Advisory
      7.      Advisory
      8.      Advisory
      9.      Advisory
      10.      Advisory
      11.      Advisory
      12.      Advisory
      13.      Advisory
      14.      Advisory
      15.      Advisory
      16.      Advisory
      17.      Advisory
      18.      Advisory
      19.      Advisory
      20.      Advisory
      21.      Advisory
      22.      Advisory
      23.      Advisory
      24.      Advisory
      25.      Advisory
      26.      Advisory
      27.      Advisory
      28.      Advisory
      29.      Advisory
      30.      Advisory
      31.      Advisory
      32.      Advisory
      33.      Advisory
      34.      Advisory
      35.      Advisory
      36.      Advisory
  6. 4Silicon Revision B Usage Notes and Advisories
    1. 4.1 Silicon Revision B Usage Notes
    2. 4.2 Silicon Revision B Advisories
      1.      Advisory
      2.      Advisory
      3.      Advisory
      4.      Advisory
      5.      Advisory
      6.      Advisory
      7.      Advisory
      8.      Advisory
      9.      Advisory
  7. 5Documentation Support
  8. 6Trademarks
  9. 7Revision History

Advisory

GPIO: Open-Drain Configuration May Drive a Short High Pulse

Revisions Affected

B, C

Details

Each GPIO can be configured to an open-drain mode using the GPxODR register. However, an internal device timing issue may cause the GPIO to drive a logic-high for up to 0–10 ns during the transition into or out of the high-impedance state.

This undesired high-level may cause the GPIO to be in contention with another open-drain driver on the line if the other driver is simultaneously driving low. The contention is undesirable because it applies stress to both devices and results in a brief intermediate voltage level on the signal. This intermediate voltage level may be incorrectly interpreted as a high level if there is not sufficient logic-filtering present in the receiver logic to filter this brief pulse.

Workarounds

If contention is a concern, do not use the open-drain functionality of the GPIOs; instead, emulate open-drain mode in software. Open-drain emulation can be achieved by setting the GPIO data (GPxDAT) to a static 0 and toggling the GPIO direction bit (GPxDIR) to enable and disable the drive low. For an example implementation, see the code below.

           
void main(void)
{ ...
  
  // GPIO configuration
     EALLOW;                               // disable pullup
     GpioCtrlRegs.GPxPUD.bit.GPIOx = 1;    // disable open-drain mode
     GpioCtrlRegs.GPxODR.bit.GPIOx = 0;    // set GPIO to drive static 0 before
                                           // enabling output
     GpioDataRegs.GPxCLEAR.bit.GPIOx = 1;
     EDIS;
  ...
  
  // application code
  ...
  
  // To drive 0, set GPIO direction as output
     GpioCtrlRegs.GPxDIR.bit.GPIOx = 1;
  
  // To tri-state the GPIO(logic 1),set GPIO as input
     GpioCtrlRegs.GPxDIR.bit.GPIOx = 0;
}