rtd cpuModule CMX147786HX, Руководство пользователя

Страница: 89 / 114

CMX147786HX RTD Embedded Technologies, Inc.
81
Real Time Clock and CMOS Memory
Overview
The cpuModule is equipped with a Real Time Clock (RTC) which provides system date and time
functions. When the cpuModule is turned off, a battery must be attached to the utility connector to
provide power to the RTC. Without power, the RTC will lose the date/time information when the
system is turned off.
The RTC also provides an "alarm" function. This may be used to generate an interrupt at a particular
time and date. This feature is commonly used to wake up the system from Sleep/Standby to run a
scheduled task (defragment the hard drive, back up files, etc).
In addition to the date/time/alarm functions, the RTC contains several bytes of battery-backed RAM,
commonly called CMOS memory. In a typical desktop PC, the CMOS memory is used by the BIOS
to store user settings. This RTD cpuModule uses onboard flash to store user BIOS settings. To pre-
serve compatibility with traditional PCs, the RTD Enhanced BIOS also mirrors the user settings
from flash in CMOS. Therefore, the contents of CMOS may be overwritten at boot time, and should
be treated as "read only".
Accessing the RTC Registers
You may access the RTC date/time and CMOS memory using the Index and Data Registers located
at I/O addresses 70h and 71h.
• Address 70h is the Index register. It must be written with the number of the register to read
or write. Valid values are 00h to 7Fh.
• Address 71h is the Data register. It contains the contents of the register pointed to by the
Index.
To read/write an RTC register, you must first set the Index register with the register number, and
then read/write the Data register.
A list of key RTC registers is shown below:
Table 35: Real Time Clock Registers
Register
Number (Hex)
Description
00 RTC Seconds
01 RTC Alarm Seconds
02 RTC Minutes
03 RTC Alarm Minutes
04 RTC Hours
05 RTC Alarm Hours