Resistive pull up as drive mode of bidirectional pin | Cypress Semiconductor
Resistive pull up as drive mode of bidirectional pin
During a certain SPI communication, I need my bidirectional SDAT pin to act as a resistive pull-up when in input. However, configuring the pin as such didn't show any pull-up in the oscilloscope.
In the past, I had the same pin used as MISO in a full-duplex SPI bus and I could correctly configure it as pull-up and see with oscilloscope that once the bus becomes high impedence, it is (slowly) pulled up to 1.
However, now that I decided to have a half-duplex SPI bus, I configured that pin as a bidirectional and set the drive mode as again resistive pull-up, but now when the bus becomes high impedence (so on the master side I have SPIM_TxDisable() and the slave is open drain), the bus actually gradually goes to 0.
Is there something preventing a bidirectional pin to behave as resistive pull-up in input? If not, what could I be doing wrong? Is there some special setting I might have missed? Again, I had no problem with setting the drive mode of an input pin as resistive pull-up, the problem only arises with a bidiectional pin.