microbit 的引脚pin0数字写入1后，不能保持，会自动归0？

模拟器上显示的和实际不一样，我用a b连个按键控制切换，模拟器上很顺畅，跟预想的一样。实际运行却始终保持 0,莫非我的板子坏了？求助大神


def on_button_pressed_a():
    pins.digital_write_pin(DigitalPin.P0, 1)
input.on_button_pressed(Button.A, on_button_pressed_a)

def on_button_pressed_b():
    pins.digital_write_pin(DigitalPin.P0, 0)
input.on_button_pressed(Button.B, on_button_pressed_b)

digi = 0
basic.show_icon(IconNames.HEART)
pins.digital_write_pin(DigitalPin.P0, 1)

def on_forever():
    global digi
    digi = pins.digital_read_pin(DigitalPin.P0)
    if digi == 1:
        basic.show_icon(IconNames.YES)
        basic.pause(500)
        basic.show_string("" + str((digi)))
        basic.pause(500)
    else:
        basic.show_icon(IconNames.NO)
        basic.pause(500)
        basic.show_string("" + str((digi)))
        basic.pause(500)
basic.forever(on_forever)