Programming Model

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

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Motorola MVME172 manual Initialization