PS-side MIO 26 is reserved as an input to the PMU for indicating a warm boot. PS bank 501 MIO26 (U1.A34) is connected to the I2C0 U15 TCA6416A bus expander (port P02 U15.6) through level-shifter U27. Refer to the Zynq UltraScale+ Device Technical Reference Manual (UG1085) for details about the PMU interface.