Specifications

7.4 Battery backed SRAM
The board can be fitted with 512K to 2 Mbytes of Static RAM. This SRAM is non volatile as data
can be automatically retained via the on-board battery when the board is not powered. The
memory is connected to the CSB5 X-Bus interface and is accessible via a paged 512 Kbyte
window (refer to Figure 7-1). Memory allocated to the window is selected via a combination of
device and page within that device. Two dedicated registers provide these functions. The page
memory and type are selected via the Memory Page and Status register. The specific device is
selected via Status & Control Register 4. The device selection gives access to each of up to four
16 Mbyte devices, thus the first 16MB is device 0, and so forth. An additional 2 Mbyte window is
also provided specifically for SRAM to permit easy access to the entire 2 Mbytes space. Refer to
Figure 7-1.
A jumper is provided (see Figure 7-3) to disconnect the backup supply to the SRAM to extend
the battery life for CMOS settings. The jumper must be fitted to permit data retention. When the
board is installed in a VME backplane which provides power via the 5V STANDBY pin, this
supply will be used in place of the on-board battery supply. However, the jumper must still be
fitted to enable this supply.
If required, the Battery Backed SRAM can be programmed with a disk image and configured via
BIOS Setup screens to operate as a RAM disk, replacing drive B:. Refer to section 4.4 for further
details.
Memory
VP 110/01x 7-5
LK3 SRAM
Backup Power
Battery
None
Figure 7-3 SRAM Backup Power Jumper