Motorola MVME172 - Manual (Page 327)

Programming Model
http://www.mcg.mot.com/literature 5-37
5
initialized by power-up, soft, or local reset to match the
NOCACHE bit in the reset serial bit stream. It should
always be left at the default value of 1.
TVECT TVECT makes bidirectional signals work while running
the vendors test vectors on this chip. It should be cleared
for normal operation. It is initialized by power-up, soft, or
local reset, to match the TVECT bit from the reset serial
bit stream.
REFDIS When REFDIS is set, refreshing is disabled. This mode
should only be used for testing, as DRAM must have
refresh to operate correctly. REFDIS is initialized by
power-up, soft, or local reset to match the REFDIS bit in
the reset serial bit stream.
XY_FLIP When XY_FLIP is set, the opposite internal set of cache
latches is selected. This bit should be used with caution
and is for test vector coverage improvement.
FRC_OPN When FRC_OPN is set, the internal DRAM read latches
are forced continuously open. This bit should be used with
caution and is for test vector coverage improvement.
Initialization
Most DRAM vendors require that the DRAMs be subjected to some
number of access cycles before the DRAMs are fully operational. The
MCECC does not perform this automatically but depends on software to
perform enough dummy accesses to DRAM to meet the requirement. The
number of required cycles is less than 10. If there are multiple blocks of
DRAM, software has to perform at least 10 accesses to each block.
The MCECC pair provides a fast zero fill capability. The sequence shown
below performs such a zero fill. It zeros all of the DRAM controlled by this
MCECC pair at the rate of 100 MB/second when the BCLK pin is