
Introduction
1-6
82801AA and 82801AB Datasheet
RTC
The ICH contains a Motorola* MC146818A-compatible real-time clock with 256 bytes of battery-
backed RAM.
The real-time clock performs two key functions:
keeping track of the time of day
and storing system data, even when the system is powered down.
The RTC operates on a
32.768 KHz crystal and a separate 3V lithium battery that provides up to 7 years of protection.
The RTC also supports two lockable memory ranges.
By setting bits in the configuration space,
two 8-byte ranges can be locked to read and write accesses.
This prevents unauthorized reading of
passwords or other system security information.
The RTC also supports a date alarm, that allows for scheduling a wake up event up to 30 days in
advance, rather than just 24 hours in advance.
GPIO
Various general purpose inputs and outputs are provided for custom system design.
The number of
inputs and outputs varies depending on ICH configuration.
Enhanced Power Management
The ICH’s power management functions include enhanced clock control, local and global
monitoring support for 14 individual devices, and various low-power (suspend) states (e.g.,
Suspend-to-DRAM and Suspend-to-Disk). A hardware-based thermal management circuit permits
software-independent entrance to low-power states.
The ICH contains full support for the
Advanced Configuration and Power Interface (ACPI) Specification.
System Management Bus (SMBus)
The ICH contains an SMBus Host interface that allows the processor to communicate with SMBus
slaves. This interface is compatible with most I
2
C devices. Special I
2
C commands are implemented
(e.g., the I
2
C Read that allows the ICH to perform block reads of I
2
C devices).
The ICH’s SMBus host controller provides a mechanism for the processor to initiate
communications with SMBus peripherals (slaves). The host controller supports seven SMBus
interface command protocols for communicating with SMBus slave devices (see System
Management Bus Specifications, Rev 1.0): Quick Command, Send Byte, Receive Byte, Write
Byte/Word, Read Byte/Word, Process Call, and Block Read/Write.