MC68030 Datasheet, PDF (311/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Memory Management Unit
9.5.1.10 LONG-FORMAT INDIRECT DESCRIPTOR. The long-format invalid descriptor is
used in pointer and page tables that contain long-format descriptors. It is used in the same
way as the short-format invalid descriptor in the preceding section. The first long word
contains the DT field in the lowest order bits. The second long word is an unused field, also
available to the operating system. Figure 9-16 shows the format of the long-format invalid
descriptor.
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Figure 9-16. Long-Format Invalid Descriptor
9.5.1.11 SHORT-FORMAT INDIRECT DESCRIPTOR. The short-format indirect descriptor
does not have a unique descriptor-type code. Rather, it resides in a page table (the bottom
level of the address translation tree) that contains short-format descriptors and is neither a
page descriptor nor an invalid descriptor. The descriptor-type field contains either the code
for a valid 4-byte descriptor or for a valid 8-byte descriptor, depending upon the size of the
referenced page descriptor. The field descriptions in 9.5.1.1 Descriptor Field Definitions
apply to the corresponding fields of this descriptor. Figure 9-17 shows the format of a short-
format indirect descriptor.
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Figure 9-17. Short-Format Indirect Descriptor
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MC68030 USER’S MANUAL
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