cs5535 National Semiconductor Corporation, cs5535 Datasheet - Page 146

• Manufacturer Part Number: cs5535
• Description: Geode Cs5535 Companion Multi-function South Bridge
• Manufacturer: National Semiconductor Corporation

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4.15 GENERAL PURPOSE INPUT/OUTPUT
Proper use and understanding of the General Purpose
Input/Output (GPIO) subsystem is the key to applying the
CS5535 in a custom system design. By totalizing the
optional features of the CS5535 GPIOs, system functions
such as soft buttons, DDC monitoring, timers, system inter-
rupts, and others, may be implemented. The system
designer should pay careful attention to the suite of fea-
tures available through the GPIO subsystem and, because
the GPIOs are multiplexed with other on-chip functions,
must make careful trade-offs to obtain the features desired
in the system.
The register space for control of the GPIO subsystem con-
tains space for control of 32 GPIOs. Since only 28 GPIOs
are realized, the control bits for the non-existent
GPIO[31:29], and GPIO[23] are marked “Reserved”.
GPIO[22:16] are multiplexed with the LPC bus; therefore, if
the system requires an LPC bus, GPIO[22:16] are not
available as GPIOs. Likewise, GPIO[15:14] are multiplexed
with the SMB (System Management Bus); if the system
requires the SMB, GPIO[15:14] will be dedicated to this
function and not available as GPIOs. Other GPIOs are mul-
tiplexed with individual functions as indicated in Table 2-8
"GPIO Options" on page 42.
Features
• Input Features:
• Output Features:
• Auxiliary Functions
— Each of the available GPIOs may be configured as
— Each of the available 28 GPIOs has a configurable
— As indicated in Table 2-8 "GPIO Options" on page 42,
— Most of the 28 GPIOs have additional hard-wired
an input. A block of eight Input Conditioning Func-
tions, providing edge detection, event counting, and
input filtering, may be configured for use by any eight
of the 28 GPIOs, though all 28 may have edge detec-
tion. The optionally-conditioned input may then be
fed to steering logic that can connect it to an inter-
rupt, or power-management input event (PME).
output cell. The output cell for each GPIO may be
independently configured to provide a variety of inter-
face options. The cell may be enabled or disabled,
configured as a totem-pole or open-drain type, have
internal pull-up or pull-down resistors applied, or be
inverted.
the GPIOs have differing output driver types and
reset defaults. When choosing a GPIO for a given
function, choose one with a compatible output driver
type, and one that the use of, does not make another
desired function inaccessible. Careful study of this
table will assist the system designer in making proper
selections of the desired functionality of the suite of
GPIOs.
internally-connected functions that may be selected
by choosing either the AUX_1 or AUX_2 outputs. Use
of these allows internal functions to be accessed at
the device pins. Table 2-8 "GPIO Options" on page
42 identifies these auxiliary functions, including
access to the UARTS and multi-function timers, as
well as certain power-management controls.
146
• Output Mapping:
• Power Domains:
• Auto-Sense:
• Recommended Functions:
— After passing through the optional input conditioning
— The GPIO circuits are distributed into the Working
— GPIO5 and GPIO6 have a feature called Auto-sense.
— System designers at National Semiconductor have
circuits, any GPIO may be mapped (connected) to
one of eight PIC-level interrupts, or to one of eight
Power Management Event (PME) inputs. A given
GPIO may not be simultaneously mapped to both an
interrupt and a PME. The PIC subsystem interrupt
inputs may be configured to cause the generation of
an ASMI-type interrupt from any or all of the mapped
GPIO signals.
and Standby power domains. Those circuits in the
Standby power domain may be used for system
wakeup events, since they remain powered when the
Working power is removed. As indicated in Table 2-8
"GPIO Options" on page 42, GPIO[28:24] are located
in the Standby power domain; all others are in the
Working power domain. Event/Filter pairs 6 and 7
are located in the Standby domain; pairs [5:0] are in
the Working power domain.
When reset is applied to the system, a weak internal
pull-up is applied to the pad. When reset is de-
asserted, the auto-sense value is used to establish
the pull-up/down state on the de-assertion edge. If
nothing pulls down the pad, then the weak pull-up
continues to be applied. If the pad is pulled down,
then pull-up is set to “no” and pull-down is set to
“yes”. The output driver does not actively drive the
pad, that is, it remains in TRI-STATE mode. If an
auto-sensed pull-down is desired, a diode between
the reset signal and the GPIO pin will pull it down
during the Auto-Sense operation but will have no
effect during normal operation.
created a list of recommended uses for selected
GPIOs, see Table 2-8 "GPIO Options" on page 42.
The desired functions were matched up with GPIOs
by selecting appropriate buffer types and multiplexing
options to create an optimal list of recommended
uses for the GPIOs. Designers may use these
recommended functions as a starting point and make
modifications to the list as needed to fit the particu-
lars of their system.
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