MVME5100 Single Board Computer Programmer's Reference Guide

SDRAM Size
I 2 C EEPROMs
Software Considerations
The SDRAM size control bits come up from power-up reset cleared to
zero. Once software has determined the correct size for an SDRAM block,
it should set the block’s size bits to match. The value programmed into the
size bits tells the Hawk how big the block is (for map decoding), and how
to translate that block’s 60x addresses to SDRAM addresses.
Programming a block’s size to non-zero also allows it to participate in
scrubbing if scrubbing is enabled.
After software programs the size bits, it should wait for a refresh to happen
before beginning to access SDRAM.
Most of the information needed to program the SDRAM speed attributes
and size is provided by EEPROM devices that are connected to Hawk’s
I 2 C bus. The EEPROM devices contain data in a specific format called
Serial Presence Detect (SPD).
SDRAM Base Address and Enable
Each block needs to be programmed for a unique base address that is an
even multiple of its size. Once a block’s speed attributes, size, and base
address have been programmed and time for at least one refresh has
passed, it can be enabled.
http://www.motorola.com/computer/literature 3-77
3