Saturday, 24 October 2009 14:38
M. Ganesh Raaja
Question: What is the difference between the HighZ and HighZ Analog drive modes?
Answer: The block diagram of the Input section of a GPIO cell is shown below.
The input path has a Schmitt trigger that interfaces the physical GPIO pin to the internal data bus. In HighZ mode, this Schmitt trigger is enabled, thus connecting the pin to the internal data bus. So, for using a pin as a digital input, HighZ mode should be used. If HighZ Analog mode is selected, the internal data bus will always read a logic LOW irrespective of the voltage level on the GPIO pin.
In HighZ Analog mode, this Schmitt Trigger is disabled. This reduces oscillations on the Schmitt Trigger output when the analog input is at the Schmitt Trigger threshold. So, to use a pin as analog input or output, select HighZ Analog drive mode.
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Saturday, 24 October 2009 14:20
M. Ganesh Raaja
Question: How do I change the drive mode of a PSoC 1 GPIO on the fly?
Answer: The drive mode of the GPIO pin can be changed on the fly by changing the PRTxDMx registers. There are three drive mode registers for each port that control the drive mode of the pins in a particular port. These are the PRTxDM0, PRTxDM1 and PRTxDM2 registers. The combination of the bits of these three registers decide the drive mode of a particular pin. The following table shows the various combinations of the PRTxDMx bits and the corresponding drive modes.
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Saturday, 24 October 2009 11:04
M. Ganesh Raaja
Question: Can I use P2[4] as External AGND by enabling the Agnd Bypass parameter in the Global Resources?
Answer: Using P2[4] as AGND is not advisable as this does not provide a low impedance path to the internal AGND. There is a 16.2K resistance between P2[4] and the actual AGND inside the PSoC. Refer the diagram below that shows the PSoC1 Reference Generator.
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