MC68EC040RC20A Freescale Semiconductor, MC68EC040RC20A Datasheet - Page 66

• Manufacturer Part Number: MC68EC040RC20A
• Description: IC MPU 32BIT 20MHZ 179-PGA
• Manufacturer: Freescale Semiconductor

Specifications of MC68EC040RC20A

• Processor Type: M680x0 32-Bit
• Speed: 20MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 179-PGA
• Lead Free Status / RoHS Status: Contains lead / RoHS Compliant
• Features: -

Using the indirection capability, single entries or entire tables can be shared between
multiple tasks. Figure 3-14 illustrates two tasks sharing a page using indirect descriptors.
When the M68040 has completed a normal table search, it examines the PDT field of the
last entry fetched from the page tables. If the PDT field contains an indirect ($2) encoding,
it indicates that the address contained in the highest order 30 bits of the descriptor is a
pointer to the page descriptor that is to be used to map the logical address. The processor
then fetches the page descriptor from this address and uses the physical address field of
the page descriptor as the physical mapping for the logical address.
The page descriptor located at the address given by the indirect descriptor must not have
a PDT field with an indirect encoding (it must be either a resident descriptor or invalid).
Otherwise, the descriptor is treated as invalid, and the M68040 creates an ATC entry with
a signaled error condition (R-bit in MMUSR is clear).
MOTOROLA
SUPERVISOR
MODE
ADDRESS OFFSET =
TABLE ENTRY # =
$76543210 =
0 1 1 1 0 1 1 0 0 1 0 1 0 1 0 0 0 0 1 X X X X X X X X X X X X X
SRP
ROOT INDEX
Freescale Semiconductor, Inc.
Figure 3-13. Example Translation Table
$EC
For More Information On This Product,
$3B
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Go to: www.freescale.com
M68040 USER'S MANUAL
ROOT LEVEL
POINTER INDEX
TABLE $00
$00001800
TABLES
$15
$54
LOGICAL ADDRESS
PAGE INDEX
$15
$01
$04
POINTER LEVEL
TABLE $3B
TABLE $00
$00003000
TABLE $7F
TABLES
PAGE OFFSET
$01
FRAME ADDRESS
PAGE LEVEL
TABLE $15
TABLE $1F
TABLE $00
TABLES
3- 17