
82801AA and 82801AB Datasheet
8-81
LPC Interface Bridge Registers (D31:F0)
8.10.4
GP_LVL—GPIO Level for Input or Output Register
Offset
GPIOBASE +0Ch
Default Value:
00200000h
Lockable:
No
Attribute:
Size:
Power Well:
R/W
32 bits
Resume
NOTES:
1. For GPI[1:0], [13:5], the active status of a GPI is read from the corresponding bit in GPE1_STS register.
2. Bit 21 defaults to 1 to allow GPIO[21] to be connected to the NOGO signal of the 82380AB PCI-TO-ISA
Bridge.
8.10.5
GPO_TTL—GPIO TTL Select Register
Offset
GPIOBASE +14h
Default Value:
06630000h
Lockable:
No
Attribute:
Size:
Power Well:
RO
32 bits
Resume
When a bit is set to 1 and the corresponding GP_IO_SEL bit is programmed as an output, the
output signal is configured as a standard high/low totem-pole driver. The output is driven high
when the corresponding GP_LVL bit is 1 and driven low when the corresponding GP_LVL bit is 0.
When a bit is 0 and the corresponding GP_IO_SEL bit is programmed as an output, the output
signal is an open-drain style driver: tri-state when the corresponding GP_LVL bit is 1 and driven
low with the corresponding GP_LVL bit is 0.
Bit
Description
31:29
Reserved. Will always be 0. Writes have no effect.
28:21
GP_LVL.
Bits 28:21 correspond to GPIO[28:21], respectively.
GPIO Programmed as Output.
If a GPIO is programmed to be an output (via the corresponding
IO_SEL bit), then the corresponding GP_LVL bit can be updated by software to drive a high or low
value on the output pin.
1 = High (corresponding GPIO signal)
0 = Low (corresponding GPIO signal)
GPIO Programmed as Input.
If a GPIO is programmed as an input, and if the corresponding
GPI_INV bit is 0, then the corresponding GP_LVL bit reflects the state of the input signal. Writes to
GP_LVL bits for GPIO set up as inputs will have no effect.
1 = High (corresponding GPIO signal)
0 = Low (corresponding GPIO signal)
20:18
Reserved. Will always be 0. Writes have no effect.
17:16
GP_LVL.
Bits 17:16 correspond to GPIO[17:16], respectively. See Bits [28:21] for functional
description.
15:0
Reserved. Will always be 0. Writes have no effect.
Bit
Description
31:29
Reserved. Always 0.
28:27
Always ‘0’. These GPIOS are open-drain outputs. Writes have no effect.
26:24
Always ‘1’. These GPIOs are TTL outputs. Writes have no effect.
23
Always ‘0’. These GPIOS are open-drain outputs. Writes have no effect.
22:21
Always ‘1’. These GPIOs are TTL outputs. Writes have no effect.
20:18
Reserved. Always 0.
17:16
Always ‘1’. These GPIOs are TTL outputs. Writes have no effect.
15:0
Reserved. Always 0.