pc87317vul National Semiconductor Corporation, pc87317vul Datasheet - Page 53

• Manufacturer Part Number: pc87317vul
• Description: Pc87317vul/pc97317vul Superi/o Plug And Play Compatible With Acpi Compliant Controller/extender
• Manufacturer: National Semiconductor Corporation

4.0 Real-Time Clock (RTC) and
The RTC logical device contains two major functions: the
Real-Time Clock (RTC) and Advanced Power Control
(APC).
The RTC is a timekeeping module that provides a time of
day clock and a multi-century calendar, alarm facilities and
three programmable timer interrupts. It maintains valid time-
keeping and retains RAM contents during power-down us-
ing external battery backup power and offers RAM-Lock
schemes and Power Management options.
RTC software module is compatible with the DS1287 and
MC146818 clock chips. (The RTC module differs from
these two chips in the following feature: Port 70 is read/write
in this module, and is write-only in the DS1287 and
MC146818.)
The APC function enables automatic PC system power-
state control in response to external events, adding power
management ability to the PC host system.
Automatic Power-Up switching enables efficient use of the
PC system in applications which are typically powered up at
all times, such as telephone answering machines or fax re-
ceivers. Automatic Power-Down switching enables a con-
trolled power-down sequence when switched off by the
user.
The PC87317VUL APC module supports a variety of exter-
nal General Purpose Power Management interrupts, giving
the user software - selectable input signal definition for each
individual input. It maintains a specific Power Management
Timer for implementing operational logic and generating the
appropriate interrupt request.
The module complies with the ACPI (Rev 1.0) standard def-
inition.
Battery-Backed Register Banks and RAM
The RTC and APC module has three battery-backed regis-
ter banks. Two are used by the logical units themselves.
The host system uses the third for general purpose battery-
backed storage.
Battery-backup power enables information retention during
system power down.
The banks are:
The memory maps and register content for each of the three
banks are illustrated in Section 4.9 "REGISTER BANK TA-
BLES" on page 89.
The lower 64-byte locations of the three banks are shared.
The first 14 bytes store time and alarm data and contain
control registers. The next 50 bytes are general purpose
memory.
The upper 64 bytes of bank addresses are utilized as fol-
lows:
Bank 0 - General Purpose Register Bank
Bank 1 - RTC Register Bank
Bank 2 - APC Register Bank
Bank 0 supplies an additional 64 bytes of memory
backed RAM.
Bank 1 uses the upper 64 bytes for functions specific
to the RTC activity and for addressing Upper RAM.
Advanced Power Control (APC)
(Logical Device 2)
Real-Time Clock (RTC) and Advanced Power Control (APC) (Logical Device 2)
53
The active bank is selected by setting RTC Control Register
A (CRA) bits 6-4 (DV2-0). (See TABLE 4-3 "Divider Chain
Control and Bank Selection" on page 57.)
All RTC register are accessed by an Index and a Data reg-
ister (at base address and base address+1 ). The Index reg-
ister points to the register location being accessed, and the
Data register contains the data to be transferred to or from
the register. An additional 128 bytes of battery-backed RAM
(also called upper RAM) may be accessed via a second lev-
el address: the second level uses the upper RAM Index reg-
ister at index 50h of bank 1 and the upper RAM Data
register at index 53h of bank 1.
Access to the three register banks and RAM may be locked.
For details see Section 4.5.8 "RAM Lock Register (RLR)" on
page 72.
4.1 RTC OVERVIEW
RTC operation is controlled using the control registers listed
in TABLE 4-1 "RTC Control Registers" below. These regis-
ters appear in all the RTC register banks. See Section 4.9
"REGISTER BANK TABLES" on page 89.
RTC configuration registers within the PC87317VUL store
the settings for all interface, configuration and power man-
agement options. These registers are described in detail in
Section 2.3 "THE CONFIGURATION REGISTERS" on
page 29.
The RTC employs an external crystal connected to an inter-
nal oscillator circuit or an optional external clock input, as
the basic clock for timekeeping.
Local battery-backed RAM serves as storage for all time-
keeping functions.
4.1.1
Bus Interface
The RTC function is initially mapped to the default I/O reg-
isters at addresses 70h (index) and 71h (data) within the
PC87317VUL. These registers may be reassigned, in com-
pliance with the Plug and Play requirements. See Section
2.2 "SOFTWARE CONFIGURATION" on page 28.
Index
Bank 2 uses the upper 64 bytes for functions specific
to the APC activity.
0Ah
0Bh
0Ch
0Dh
rel
rel
rel
1. These registers have relocatable indexes.
1
1
1
See register descriptions.
RTC Hardware and Functional Description
TABLE 4-1. RTC Control Registers
DMAR
Name
CRA
CRB
CRC
CRD
MAR
CR
Day-of-Month Alarm Register
RTC Control Register A
RTC Control Register B
RTC Control Register C
RTC Control Register D
Month Alarm Register
Century Register
Description
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