41.3 AT91SAM7X512 Errata - Rev. A Parts 41.3.5.3 PIO: Drive Low NRST, PA0-PA30 and PB0-PB26 When NRST or PA0 - PA30 or PB0 - PB26 are set as digital inputs with pull-up enabled, driving the I/O with an output impedance higher than 500 ohms may not drive the I/O to a logical zero. Problem Fix/Workaround Output impedance must be lower than 500 ohms.