11 Replies Latest reply on Nov 6, 2012 2:02 PM by user_14586677

    What is High Z analog or High Z digital pins

    akash.gupta

      What are high z pins?

         

      I just wanted to know what does High Z mean?? and how provides enough voltage???

        • 1. Re: What is High Z analog or High Z digital pins
          user_78878863

          "High Z" means high impedance. This is used for analog inputs, since there the impedance of the input can affect the signal level (if it is too low).

          • 2. Re: What is High Z analog or High Z digital pins
            user_2405011

            As hli said, "High Z" is for Analog Input.

               

             

               

            Here's more info on the drive modes:

               

               

            Regards,

               

            Rolf

            • 3. Re: What is High Z analog or High Z digital pins
              user_1377889

              When a pin is internally connected to an analog usermodule as amplifiers, ADCs or DACs the signal is treated differently and routed within a completely different part of the chip than when the pin is connected to a digital signal internally. Hi-Z refers to the input impedance only. When routing with Creator 2.1 your usermodules you will see different colors used for the wires: green for digital signals, orange for analog signals and blue for annotation wires outside of the chip.

                 

               

                 

              Bob

              • 4. Re: What is High Z analog or High Z digital pins
                akshay.phatak

                High Z analog drive mode should be used for any pin connected to any analog component. For eg. input of ADC, output of DACs as well as input and output of PGAs, OPAMPs.

                   

                 

                   

                High Z digital drive mode should be used for digital input pins when both logic levels are driven externally. For example, in UART, RX pin should be high z digital since TX on the other side will drive logic 0 as well as logic 1 on the line.

                   

                 

                   

                On the other hand, a pin connected to a switch which toggles between digital '0' and open circuit can not be high z digital. In this case, the drive mode should be resistive pull up to hold the voltage at logic '1' level when switch is open circuit.

                • 5. Re: What is High Z analog or High Z digital pins
                  user_14586677

                  Hi Z, as you can see from the schematic pic in earlier post, means

                     

                  the source and sink drivers are turned off at the pin, and the pin is connected

                     

                  via a route to a buffer input. So the Z is routing R + buffer C in. From an

                     

                  AC point of view.

                     

                   

                     

                  From a DC point of view HiZ means basically all you are driving/absorbing is a

                     

                  leakage current, that of the buffer input and the output totem pole driver leakages.

                     

                   

                     

                  A caution you must consider is HiZ, is if source driver is also HiZ interpreting what

                     

                  will be the voltage on the pin, as this case is controlled by leakage, and device to

                     

                  device variation and temp effects will produce unpredictable values. In short be

                     

                  careful about HiZ pins driving, for example, a MOSFET or Bipolar. Leakage can

                     

                  turn these devices on when you do not want this behaviour. So terminate a HiZ pin

                     

                  under these circumstances with an R such that R x Ileak < Vth, where Vth is turnon

                     

                  V of the external device.

                     

                   

                     

                  Regards, Dana.

                  • 6. Re: What is High Z analog or High Z digital pins
                    akash.gupta

                     SO , if I have my PSOC3 connected to some other device say  PSoC5, now when i reset the PSoC3 will the pins drain some current from PSoC5 pins if not set to high Z configuration on reset????

                    • 7. Re: What is High Z analog or High Z digital pins
                      user_1377889

                      The answer is YES. Pins not configured as High-Z (which is the default) will sink or source current from its connection. When resetted the pins are in Hi-Z state and the initialization of the chip starts which includes setting the pin's drive mode and polarity which will alltogether take some miliseconds.

                         

                       

                         

                      Bob

                      • 8. Re: What is High Z analog or High Z digital pins
                        user_14586677

                        This might help -     www.cypress.com/?docID=34818

                           


                        Startup and Low-Power Behavior


                           

                        Out of the box, all GPIO pins start up in an Analog HI-Z
                        state and remain in that state until reset is released. The
                        initial operating configuration of each pin is loaded during
                        boot and takes effect at that time. The reset behavior of
                        GPIOs can be changed in PSoC 3 using the PRTxRDM
                        fields of the nonvolatile latch array, which are written when
                        the PSoC is programmed.

                           


                        In all low-power modes, GPIO pins retain their state until
                        the part is  reset or awakened. The port interrupt logic
                        continues to function in all low-power modes so that pins
                        can be used as wakeup sources.

                           


                        Regards, Dana.

                        • 9. Re: What is High Z analog or High Z digital pins
                          content.librarian

                           Hi, Im giving variable analog input(max rating 5V) to PSoC 5lp in high impedance mode.Now my question is can I directly give the potentiometer input to PSoC?How much resistance does any analog pin provide in this mode? Will the current damage PSoC? 

                             

                          Right now as precaution i have connected 1k in series with POT,Psoc is taking floating value when i switch the input near to zero volts.The reason being psoc is unable to detect ground because of that 1k ohm.

                             

                          RISHI

                          • 10. Re: What is High Z analog or High Z digital pins
                            user_78878863

                            Please, when you have a new question, ask it as such and open a new topic. Don't hijack a year-old thread, especially when it has nothing to do with your question. A new topic will increase your chance of getting a good answer.

                               

                            Btw: it can be andwered by just reading the PSoC5 data sheet, it states the properties of the analog inputs and the maximum ratings they can withstand.

                            • 11. Re: What is High Z analog or High Z digital pins
                              user_14586677

                              As long as you conform to ~ Vdda >= Vin >= Vssa as an input to

                                 

                              an analog pin you are OK. Consult specs on module as some

                                 

                              modules actually have a little expanded range. eg. inputs can

                                 

                              go below Vssa a few hundred mV.

                                 

                               

                                 

                              If you have a Vin outside these ranges you handle this by -

                                 

                               

                                 

                              1) Limiting current in via a resistor, spec for injection current in datasheet.

                                 

                              OR

                                 

                              2) Use clamps on pins + an R. Schotky diode best, silicon diode

                                 

                              in most designs.

                                 

                               

                                 

                              Regards, Dana.