MOTOROLA
M68060 USER’S MANUAL
4-1
SECTION 4
MEMORY MANAGEMENT UNIT
NOTE
This section does not apply to the MC68EC060. Refer to
Appendix B MC68EC060
for details.
The MC68060 supports a demand-paged virtual memory environment. Demand means that
programs request permission to use memory area by accessing logical addresses, and
paged means that memory is divided into blocks of equal size, called page frames. Each
page frame is divided
into pages of the same size. The operating system assigns pages to
page frames as they are required to meet the needs of the program.
The MC68060 memory management includes the following features:
• Independent Instruction and Data Memory Management Units (MMUs)
• 32-Bit Logical Address Translation to 32-Bit Physical Address
• User-Defined 2-Bit Physical Address Extension
• Addresses Translated in Parallel with Indexing into Data or Instruction Cache
• 64-Entry Four-Way Set-Associative Address Translation Cache (ATC) for Each MMU
(128 Total Entries)
• Global Bit Allowing Flushes of All Nonglobal Entries from ATCs
• Selectable 4- or 8-Kbyte Page Size
• Separate Supervisor and User Translation Tables
• Two Independent Blocks for Each MMU Can Be Defined as Transparent (Untranslated)
• Three-Level Translation Tables with Optional Indirection
• Supervisor and Write Protections
• History Bits Automatically Maintained in Descriptors
• External Translation Disable Input Signal (MDIS) for Emulator Support
• Caching Mode Selected on Page Basis
• Default Transparent Translation
• Default Cache Mode and User Attributes
The MMUs completely overlap address translation time with other processing activities
when the translation is resident in the corresponding ATC. ATC accesses operate in parallel
with indexing into the on-chip instruction and data caches. The MMU MDIS signal dynami-
cally disables address translation for emulation and diagnostic support.
