The second size register specifies the combined size of the NRAS[1:0] devices that are mapped into CPU address space. The 3-bit value may be configured to any multiple of 128 KB between 0 KB and 640 KB. Given these two values, the start and end addresses for both NRAS[0] and NRAS[1] can be determined.
The size register value only specifies the amount of RAM that is mapped into the CPU address space. It does not indicate the amount of RAM that is physically available on NRAS[1:0].
The size of NRCE is fixed at 160 KB. (See page 15-498.)
Size Register Value = (Device Size / 131072)
Index Name Reset Comments
Value
===================================================================
-84h Device Size Reg0 01h Size of NRAS[0] (128KB default)
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-85h Device Size Reg1 01h Combined size of NRAS[1:0]
(128 KB default)
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The above reset values result in a size of 0 KB for NRAS[1]. Whenever Device Size Reg0
and Device Size Reg1 contain the same value, the specified memory is mapped entirely into
NRAS[0]. If Device Size Reg0 contains a value that is larger than the value in Device
Size Reg1, the memory size given by Device Size Reg0 is assumed correct and the specified
memory is again mapped entirely into NRAS[0]. To map the specified memory entirely into
NRAS[1], Device Size Reg0 must contain the value of 00h and Device S ize Reg1 must
contain a value greater than 00h.If a device is configured with a size that is larger than its actual size, several images of the device will appear in the allotted address space.