CME34M Hardware Manual - RTD Embedded Technologies, Inc.
CME34M Hardware Manual - RTD Embedded Technologies, Inc.
CME34M Hardware Manual - RTD Embedded Technologies, Inc.
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Real Time Clock Control<br />
Overview<br />
The cpuModule is equipped with a Real Time Clock (RTC) which provides system date and time functions.<br />
When the cpuModule is turned off, a battery must be attached to the utility connector to provide power to the<br />
RTC. Without power, the RTC will lose the date/time information when the system is turned off.<br />
The RTC also provides an “alarm” function. This may be used to generate an interrupt at a particular time and<br />
day. This feature is commonly used to wake up the system from Sleep/Standby to run a scheduled task<br />
(defragment the hard drive, back up files, etc.).<br />
In addition to the date/time/alarm functions, the RTC contains several bytes of battery-backed RAM, commonly<br />
called CMOS memory. In a typical desktop PC, the CMOS memory is used by the BIOS to store user settings.<br />
This <strong>RTD</strong> cpuModule uses onboard flash to store user BIOS settings. To preserve compatibility with traditional<br />
PCs, the <strong>RTD</strong> Enhanced BIOS also mirrors the user settings from flash in CMOS. Therefore, the contents of<br />
CMOS may be overwritten at boot time, and should be treated as “read only”.<br />
Accessing the RTC Registers<br />
You may access the RTC date/time and CMOS memory using the Index and Data Registers located at I/O<br />
addresses 70h and 71h.<br />
• Address 70h is the Index register. It must be written with the number of the register to read or write.<br />
Valid values are 00h to 7Fh.<br />
• Address 71h is the Data register. It contains the contents of the register pointed to by the Index.<br />
To read/write an RTC register, you must first set the Index register with the register number, and then read/write<br />
the Data register.<br />
A list of key RTC registers is shown in Table 50 below:<br />
Table 50<br />
Real Time Clock Registers<br />
Registers<br />
(hex)<br />
Registers<br />
(decimal)<br />
Function<br />
00h 0 RTC Seconds<br />
02h 2 RTC Minutes<br />
04h 4 RTC Hours<br />
06h 6 RTC Day of Week<br />
07h 7 RTC Day of Month<br />
08h 8 RTC Month<br />
09h 9 RTC Year<br />
0Ah 10 RTC Status Register A<br />
• Bit 7: RTC Update In Progress (Read Only) - RTC registers<br />
should not be accessed when this bit is high.<br />
• Bits 6-4: Divider for 32.768 KHz input (should always be 010)<br />
• Bits 3-0: Rate select for periodic interrupt.<br />
64 <strong>CME34M</strong> cpuModule BDM-610000076 Rev A