GPIO pullups and direction

Question

If I write a zero to the output register, and enable the pullup on the same pin, can I switch between driven low output and input with pullup simply by settting/clearing the DIR bit? Will the pullup still be in circuit when the output is enabled? I have studied the datasheet and the associated schematic, but this is still not clear to me.

JohnBrown · Accepted Answer

Well we'll have to agree to disagree on that, then. I haven't connected a logic analyser, but I have used a low current LED with a 220R resistor in series, and I am getting a dim glow, consistent with a pullup being enabled. Using exactly this code(LED is on P0.17) NRF_GPIO->DIRCLR = (1UL << 17); // Set as ip NRF_GPIO->PIN_CNF[17] |= GPIO_PIN_CNF_PULL_Pullup << GPIO_PIN_CNF_PULL_Pos; // Set pullup SEGGER_RTT_printf(0, "PIN_CNF = %08x ", NRF_GPIO->PIN_CNF[17]); nrf_start_timer_ms(2000); // Set timeout at 2 seconds while (NRF_TIMER1->EVENTS_COMPARE[0] == 0) { } NRF_GPIO->DIRSET = (1UL << 17); // Set as op SEGGER_RTT_printf(0, "PIN_CNF = %08x ", NRF_GPIO->PIN_CNF[17]); nrf_start_timer_ms(2000); // Set timeout at 2 seconds while (NRF_TIMER1->EVENTS_COMPARE[0] == 0) { } NRF_GPIO->DIRCLR = (1UL << 17); // Set as ip SEGGER_RTT_printf(0, "PIN_CNF = %08x ", NRF_GPIO->PIN_CNF[17]); while(1); John

GPIO pullups and direction

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