GPIO19 and Card Reset
GPIO19 is special in that it is intended to be used as the "Card Reset" signal for PCMCIA cards. GPIO19 has special hardware to tri-state it during reset but also needs some special handling by software. If GPIO19 is used as the PCMCIA card reset (CRST) signal, the following guidelines should be followed:
- CRST should be tri-stated on entry into deep sleep and on entry into backup. In this state we are ready for powerup. [Powerup = exit from deep sleep or backup].
- CRST should be tri-stated whenever there is no card present. In this state we are ready for a hot insertion.
- CRST should be driven high starting 1ms or more after powerup if a card is present. After a 10us (minimum) high time, it should be driven low.
- CRST should be driven high starting 1ms or more after a card is hot inserted. After a 10us high time, it should be driven low.
- The card chip enable (NCS[1:0]) should not be activated for a minimum of 20 mS following the end of reset.