ST90158 - DEVICE ARCHITECTURE
ADDRESS SPACE EXTENSION (Cont’d)
2.6.2 Addressing 64-Kbyte Segments
Most of these registers do not have a default value
after reset.
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).
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.
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 Figure 15).
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.
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.
Data Page Register relocation is illustrated in Fig-
ure 13.
Figure 15. Addressing via CSR, ISR, and DMASR
16-bit virtual address
MMU registers
ISR
DMASR
CSR
1
2
3
1
2
Fetching program
instruction
Data Memory
accessed in DMA
6 bits
Fetching interrupt
instruction or DMA
3
access to Program
Memory
22-bit physical address
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