SMSC LAN9311i - Manual (Page 194)

Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08) 194 SMSC LAN9311/LAN9311i
DATASHEET
11:0 GPIO Buffer Type 11-0 (GPIOBUF[11:0])
This field sets the buffer types of the 12 GPIO pins.
0: Corresponding GPIO pin configured as an open-drain driver
1: Corresponding GPIO pin configured as a push/pull driver
As an open-drain driver, the output pin is driven low when the corresponding
data register is cleared, and is not driven when the corresponding data
register is set.
As an open-drain driver used for 1588 Clock Events, the corresponding
GPIO_EVENT_POL_8 and GPIO_EVENT_POL_9 bits determine when the
corresponding pin is driven per the following table:
R/W 0h
BITS DESCRIPTION TYPE DEFAULT
GPIOx Clock Event Polarity 1588 Clock Event Pin State
0 no not driven
0 yes driven low
1 no driven low
1 yes not driven