Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
941
General Purpose I/O Unit—Intel
®
81341 and 81342
17.0
General Purpose I/O Unit
This chapter describes the Intel
®
81341 and 81342 I/O Processors (81341 and 81342)
General Purpose I/O Unit; operation modes, setup, external memory interface, and
implementation of General Purpose I/Os (GPIOs).
17.1
General Purpose Input Output Support
Twelve pins are provided as General Purpose Input Output (GPIO) pins. The Twelve pins
are
GPIO[15:0]
. These pins can be used by the Intel XScale
®
processors to control or
monitor external devices in the I/O subsystem.
17.1.1
General Purpose Inputs
The current state of the twelve GPIO pins can be read in
HPI#
.
Note:
When configured as GPIOs, the twelve GPIO pins can be used as (up to) 12 additional
external interrupt inputs dedicated to the Intel XScale
®
processor. This feature is
available on a per pin basis simply by programming the INTCTL[3:0] registers.
17.1.2
General Purpose Outputs
The output function of the GPIO pins is controlled by two registers, as stated in
17.2.3, “GPIO Output Data Register — GPOD” on page 946
) and
Output Enable Register — GPOE” on page 943
The output enables are mapped on a per bit basis to each of the data bits in the GPIO
Output Data Register. When a bit of the GPIO Output Enable Register is cleared, the
corresponding data bit value in the GPIO Output Data Register is actively driven on the
appropriate GPIO pin.
17.1.3
Reset Initialization of General Purpose I/O Function
• GPIO Input Data Register is initialized to the state of
GPIO[15:0]
bus upon
assertion of
P_RST#
. Note that
GPIO[3:0]
pins are multiplexed with the PCI-X
interrupts
P_INT[D:A]#
and, therefore, are initialized as output pins when the
PCI-X interface is used as an endpoint.
• GPIO Output Data Register is initialized to all zeros upon assertion of
P_RST#
.
• GPIO Output Enable Register is initialized to FFFFH upon assertion of
P_RST#
. This
means that
GPIO[15:0]
are initialize as inputs.
•
GPIO[15:0]
pins are tristated during
P_RST#
assertion.