Motorola MC68030 User Manual page 329

9.5.1.10 LONG-FORMAT INVALID DESCRIPTOR. The long-format invalid descrip-
tor 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 pre-
ceding 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.
31 2 1 0 31
UNUSED
UNUSED
Figure 9-16. Long-Format Invalid Descriptor
9.5.1.11 SHORT-FORMAT INDIRECT DESCRIPTOR. The short-format indirect de-
scriptor 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 de-
scriptor. 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. Fig-
ure 9-17 shows the format of a short-format indirect descriptor.
31 2 1 0
DESCRIPTOR ADDRESS
Figure 9-17. Short-Format Indirect Descriptor
MOTOROLA MC68030 USER'S MANUAL 9-27