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CENTRAL PROCESSING UNIT (CPU)

7721 Group User’s Manual

2–17

2.4 Memory assignment

This section describes the internal area’s memory assignment. For more information about the external

area, refer also to “CHAPTER 3. CONNECTION WITH EXTERNAL DEVICES.”

Figure 2.4.1 shows the memory assignment.

2.4.1 Memory assignment in internal area

SFR (Special Function Register) and internal RAM are assigned in the internal area.

(1)

SFR area

The registers for setting internal peripheral devices are assigned at addresses 016 to 7F16 and 1FC016

to 1FFF16. This area is called SFR. Figures 2.4.2 and 2.4.3 show the SFR area’s memory assignment.

For each register in the SFR area, refer to each functional description in this manual.

For the state of the SFR area immediately after reset, refer to section “4.1.2 State of CPU, SFR

area, and internal RAM area.”

(2)

Internal RAM area

The M37721S2BFP (Note 1) assigns the 1024-byte static RAM at addresses 8016 to 47F16. 512 bytes

of that can be selected either it is used as the internal RAM or it is used as the external area. (Note

The internal RAM area is used as a stack area (Note 3), as well as an area to store data. Accordingly,

note that set the nesting depth of a subroutine and multiple interrupts’ level not to destroy the

necessary data.

Notes 1: The M37721S1BFP assigns the 512-byte static RAM at addresses 8016 to 27F16.

2: The internal RAM area becomes 512 bytes after reset because the internal RAM area

select bit is “0.”

3: Either bank 016 or bank FF16 can be selected as the stack area by the stack bank select

bit (bit 7 at address 5E16).

Figure 2.4.4 shows the structure of the processor mode registers 0, 1.

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