HD6417750RF240DV Renesas Electronics America, HD6417750RF240DV Datasheet - Page 158

• Manufacturer Part Number: HD6417750RF240DV
• Description: MPU 3V 16K I-TEMP,PB-FREE 208-QF
• Manufacturer: Renesas Electronics America
• Series: SuperH® SH7750r

Specifications of HD6417750RF240DV

• Core Processor: SH-4
• Core Size: 32-Bit
• Speed: 240MHz
• Connectivity: EBI/EMI, FIFO, SCI, SmartCard
• Peripherals: DMA, POR, WDT
• Number Of I /o: 28
• Program Memory Type: ROMless
• Ram Size: 48K x 8
• Voltage - Supply (vcc/vdd): 1.4 V ~ 1.6 V
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 208-QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Program Memory Size: -
• Data Converters: -

Section 3 Memory Management Unit (MMU)
of the MMU is to map a number of virtual memory areas onto physical memory in an efficient
manner. It is also provided with memory protection functions to prevent a process from
inadvertently accessing another process's physical memory.
When address translation from virtual memory to physical memory is performed using the MMU,
it may happen that the translation information has not been recorded in the MMU, or the virtual
memory of a different process is accessed by mistake. In such cases, the MMU will generate an
exception, change the physical memory mapping, and record the new address translation
information.
Although the functions of the MMU could be implemented by software alone, having address
translation performed by software each time a process accessed physical memory would be very
inefficient. For this reason, a buffer for address translation (the translation lookaside buffer: TLB)
is provided in hardware, and frequently used address translation information is placed here. The
TLB can be described as a cache for address translation information. However, unlike a cache, if
address translation fails—that is, if an exception occurs—switching of the address translation
information is normally performed by software. Thus memory management can be performed in a
flexible manner by software.
There are two methods by which the MMU can perform mapping from virtual memory to physical
memory: the paging method, using fixed-length address translation, and the segment method,
using variable-length address translation. With the paging method, the unit of translation is a
fixed-size address space called a page (usually from 1 to 64 Kbytes in size).
In the following descriptions, the address space in virtual memory in the SH-4 is referred to as
virtual address space, and the address space in physical memory as physical address space.
Rev.7.00 Oct. 10, 2008 Page 72 of 1074
REJ09B0366-0700