7 Replies Latest reply on Sep 9, 2020 8:03 PM by JayakrishnaT_76

    About PMODE pin condition

    NoAr_1540581

      Hello

       

      Regarding FX3/CX3 PMODE pin for setting boot option.
      Please tell me the input condition when changing the setting of boot mode due to the external input and setting the set value to "0", "Hi-Z", "1 "from the set condition.
      Is the terminal a circuit with a 3-state input and 1/2VIN when open due to the internal resistance voltage division of the input stage?

       

      Best Regards

      Arai

       

        • 1. Re: About PMODE pin condition
          JayakrishnaT_76

          Hello Arai San,

           

          When the FX3/CX3 device is reset/connected, the Bootloader will detect the status of the PMODE pins. The status will be as follows based on how the PMODE pins are connected:

          1. If a pin is pulled up, then the status of that pin will be detected as '1'.

          2. If a pin is pulled down, then the status of that pin will be detected as '0'.

          3. If a pin is left unconnected, then the status of that pin will be detected as 'Z'.

           

          Please let me know if you have any queries on this.

           

          Best Regards,

          Jayakrishna

          • 2. Re: About PMODE pin condition
            NoAr_1540581

            Hello Jayakrishna san

             

            Thank you for your reply.

            This time, They do not use DIP Sw to change tthe PMODE. PMODE is fixedly input by PU or PD according to the setting on the circuit board.
            Switching between "1", "0", and "F" is planned to be controlled by voltage dividing resistors.

            I would like to know the above PU and PD conditions and additional input conditions when I want to change the setting with this fixed input.

            Q1)  Is the input impedance of the terminal ∞, and if the constant voltage input of Vcc(1), 1/2Vcc(F), and GND(0) level is applied, shouldn't it be necessary to consider the input current?

            Q2) By the way, can you tell me the value of the internal impedance of PMODE terminal?

             

            Best Regards

            Arai

            • 3. Re: About PMODE pin condition
              JayakrishnaT_76

              Hello Arai san,

               

              Under normal conditions, the PMODE pins are not pulled up or pulled down internally. The pull-up and pull-downs are engaged by the bootloader for detecting the state of the PMODE pins. Please find the working of the bootloader for detecting the state of PMODE pins below:

               

              1. The Bootloader will initially pull up all the PMODE pins internally to HIGH voltage. The value of pull up resistor as per Page 13 of FX3 datasheet is 50Kohm. Then it will check the state of the PMODE pins.

              2. Then the bootloader will remove the pull up on PMODE lines. After this, it will pull down the PMODE lines to LOW voltage. The value of pull down resistor is 10Kohm as per page 13 of FX3 datasheet. Again it will check the state of the PMODE pins. After this, the internal pull downs are removed.

               

              This is done upon every connection/reset of device.

               

              Suppose a PMODE pin is floating (i.e left unconnected externally), then upon placing an internal pull-up, the voltage on that pin will be HIGH. Next, when an internal pull-down is placed on that pin, the voltage on that pin will be LOW. This change in the voltage level upon changing the internal pull-up and pull-down resistors is used by the bootloader to detect if the pin is floating or not. Please refer to the table 8 of FX3 datasheet to understand the range of voltages that are interpreted as HIGH and the range of voltages that are interpreted as LOW corresponding to the power domain voltage of a particular IO.

               

              Next, if a PMODE pin is pulled high externally or supplied with a high voltage externally. When an internal pull-up is placed on that pin by the bootloader, the voltage on that pin will be HIGH itself. Next, when an internal pull-down is placed, a voltage divider is formed at that pin (external resistor and internal 10K pull down). Here, care should be taken while choosing the external resistor so that the voltage at that pin does not fall into the LOW level. If it falls into the LOW level, then the bootloader will interpret that pin as floating.

               

              Next, if a PMODE pin is pulled down externally, then when an internal pull up resistor is placed on that pin by the bootloader, a voltage divider is formed (50K internal pull up and external pull down resistor). Here also, care should be taken while choosing the external resistor so that the voltage at that pin does not fall into the HIGH level. Next, when the bootloader places an internal pull down resistor on that pin, the voltage on that pin will be LOW itself. So, if the voltage at the pin when the bootloader placed an internal pull up resistance fell into the HIGH level, then the bootloader can interpret that pin as floating.

               

              Best Regards,

              Jayakrishna

              • 4. Re: About PMODE pin condition
                NoAr_1540581

                Hello Jayakrishna san

                 

                Thank you for your reply.

                Just in CASE  I want to confirm about "Hi-Z detection" based on your answer.

                When detecting Hi-Z, we are considering a circuit configuration that can detect Hi-Z by using a voltage divider resistor without floating the pins.

                Based on the answers you provided, I believe that if they can input a voltage that does not apply the input pin voltage to either Hi or Lo detection range by voltage divider resistor ( Based on the table 8 of FX3 datasheet) , it can be recognized as Hi-Z.  Is there no problem with such usage (circuit configuration) for Hi-Z detection?

                 

                Best Regards

                Arai

                • 5. Re: About PMODE pin condition
                  JayakrishnaT_76

                  Hello,

                   

                  Yes, you can use such a configuration. But make sure that when the internal pull up (50K) is attached to the PMODE lines, the voltage level on that pin falls into HIGH level. And when the internal pull down is added to the PMODE lines, the voltage level on that pin falls into LOW level. Only then it will be detected as a floating pin by the bootloader. If this condition is met properly, then you can use it.

                   

                  Best Regards,

                  Jayakrishna

                  • 6. Re: About PMODE pin condition
                    NoAr_1540581

                    Hello Jayakrishna san

                     

                    Thank you for your answer.

                     

                    Best Regards

                    Arai

                    • 7. Re: About PMODE pin condition
                      JayakrishnaT_76

                      Hello Arai san,

                       

                      Please let me know if you have anymore questions on this thread?

                       

                      Best Regards,

                      Jayakrishna