Question: What drive modes can be used for a digital input pin that is connected as an input to a digital block (such as a UART receiver) in PSoC® Designer™? Can you use a pull-up drive mode for such a digital input pin?
Only the High-Z drive mode can be used for a pin that is connected as an input to a digital block. Other drive modes, such as pull-up/pull-down, cannot be used as the drive mode of such a pin due to the architectural limitation of the GPIO pin. The PSoC 1 TRM contains the architecture of the GPIO pins.
Figure 1 shows a screenshot of this GPIO architecture, which highlights the limitation that causes only the High-Z digital drive mode option to be available for this pin.
Figure 1. GPIO Architecture