Cyclone® V Hard Processor System Technical Reference Manual

ID 683126
Date 8/28/2023
Public
Document Table of Contents

23.3.4. GPIO Pin State During Reset

Ensure you understand the state of the GPIO during a warm or cold reset.

Cold reset: HPS I/O are in tri-state with a weak pull-up. The pin multiplexer and the GPIO/LoanIO multiplexer are in the default state meaning they are set to their reset value. You can find the default, reset value in the registers of the Pin Mux Control Group.

Warm reset: HPS I/O retain their configuration. The pin multiplexer and GPIO/LoanIO Multiplexer do not change configuration during warm reset meaning they are not reset to the default, reset value but maintain the current settings. For example, the pin multiplexer determines which signals go to the pins. Thus, if a pin multiplexer is set to be a GPIO it remains as a GPIO after warm reset. And when warm reset is triggered, the GPIO block is reset and the GPIO data direction register (gpio_swporta_ddr) is reset to 0x0 which is input, meaning the HPS I/O are inputs. In summary, a warm reset retains the pin multiplexer configuration but not the direction and output level which is controlled by the GPIO block. This block is reset under warm reset.