ST92185B STMicroelectronics, ST92185B Datasheet - Page 37

• Manufacturer Part Number: ST92185B
• Description: 16k/24k/32k Rom Hcmos Mcu With On-screen-display
• Manufacturer: STMicroelectronics

ADDRESS SPACE EXTENSION (Cont’d)
2.6.2 Addressing 64-Kbyte Segments
This extension mode is used to address Data
memory space during a DMA and Program mem-
ory space during any code execution (normal code
and interrupt routines).
Three registers are used: CSR, ISR, and DMASR.
The 6-bit contents of one of the registers CSR,
ISR, or DMASR define one out of 64 Memory seg-
ments of 64 Kbytes within the 4 Mbytes address
space. The register contents represent the 6
MSBs of the memory address, whereas the 16
LSBs of the address (intra-segment address) are
given by the virtual 16-bit address (see
2.7 MMU REGISTERS
The MMU uses 7 registers mapped into Group F,
Page 21 of the Register File and 2 bits of the
EMR2 register.
Figure 18. Addressing via CSR, ISR, and DMASR
3
1
2
Fetching interrupt
Data Memory
Fetching program
instruction or DMA
access to Program
Memory
accessed in DMA
instruction
CSR
1
Figure
MMU registers
DMASR
6 bits
11).
22-bit physical address
2
Most of these registers do not have a default value
after reset.
2.7.1 DPR[3:0]: Data Page Registers
The DPR[3:0] registers allow access to the entire 4
Mbyte memory space composed of 256 pages of
16 Kbytes.
2.7.1.1 Data Page Register Relocation
If these registers are to be used frequently, they
may be relocated in register group E, by program-
ming bit 5 of the EMR2-R246 register in page 21. If
this bit is set, the DPR[3:0] registers are located at
R224-227 in place of the Port 0-3 Data Registers,
which are re-mapped to the default DPR's loca-
tions: R240-243 page 21.
Data Page Register relocation is illustrated in
ure
9.
ST92185B - DEVICE ARCHITECTURE
ISR
3
16-bit virtual address
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Fig-