RadiSys PL35Q, Product Manual, Page: 33 / 72

3
CMOS RAM and RTC
33
CMOS RAM and RTC
The chipset integrates real-time clock (RTC) and 256 bytes of CMOS RAM that is used by the
BIOS to store configuration information. A replaceable lithium cell battery (type CR2032) backs
up both the RTC and the CMOS RAM, and provides approximately 5 years of un-powered
backup.
When available, the RTC and CMOS RAM are powered from the +3.3V standby power rather
than the lithium battery cell. The system management hardware can monitor the lithium cell
voltage directly.
One 1x3-pin Clear CMOS jumper is available to clear the CMOS from the BIOS RAM. By default,
pins 1 and 2 are jumpered for normal system operation. To clear the CMOS, jumper pins 2 and
3.
W
ARNING
!
For an ATX power supply, you must completely shut down the system, remove the AC
power cord and then clear the CMOS.
Firmware hub (FWH)
Q35 motherboards provide a 2MB Firmware Hub (FWH) via the SPI bus. The FWH uses the
Intel FWH protocol and does not require an ISA bus. The BIOS ROM is stored in a 2MB flash
memory chip. The system BIOS provides support for all functions and devices present on the
Q35 motherboards.