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PSoC 5, 3 & 1 MCU

Anonymous
Not applicable

What are high z pins?

   

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

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11 Replies
Honored Contributor II

"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).

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Contributor II

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

   

 

   

Here's more info on the drive modes:

   

   

Regards,

   

Rolf

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Esteemed Contributor II

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

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Anonymous
Not applicable

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.

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Esteemed Contributor

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.

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Anonymous
Not applicable

 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????

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Esteemed Contributor II

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

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Esteemed Contributor

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.

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Anonymous
Not applicable

 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

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Honored Contributor II

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.

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Esteemed Contributor

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.

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