MC68030 Datasheet, PDF (310/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Memory Management Unit
9.5.1.7 SHORT-FORMAT PAGE DESCRIPTOR. The short-format page descriptor is used
in the page tables (the bottom level of the address table). The field descriptions in 9.5.1.1
Descriptor Field Definitions apply to the corresponding fields of this descriptor. The short-
format page descriptor is identical to of the short-format early termination page descriptor
shown in Figure 9-12.
9.5.1.8 LONG-FORMAT PAGE DESCRIPTOR. The long-format page descriptor is also
used in the page tables. The field descriptions in 9.5.1.1 Descriptor Field Definitions apply
to the corresponding fields of this descriptor. Figure 9-14 shows the format of the long-
format page descriptor.
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Figure 9-14. Long-Format Page Descriptor
9.5.1.9 SHORT-FORMAT INVALID DESCRIPTOR. The short-format invalid descriptor
consists of a DT field that contains zeros, identifying it as an invalid descriptor. It can be used
at any level of the address translation tree except at the root pointer level. The 30-bit unused
field is available to the operating system to identify unallocated portions of the table or
portions of the table that reside on an external device. For example, the disk address of disk-
resident tables or pages can be stored in this field. Figure 9-15 shows the format of a short-
format invalid descriptor.
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Figure 9-15. Short-Format Invalid Descriptor
9-22
MC68030 USER’S MANUAL
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