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7906 Group User’s Manual Rev.2.0

2-15

CENTRAL PROCESSING UNIT (CPU)

2.4 Memory assignment

This section describes the memory assignment in the internal area.

2.4.1 Memory assignment in internal area

SFR (Special Function Register), internal RAM, and internal ROM are assigned to the internal area. Figure

2.4.1 shows the memory assignment in the internal area.

(1)

SFR area

The registers used to set the internal peripheral devices are assigned to addresses 016 to FF16. 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 “3.3 State of internal area.”

(2)

Internal RAM area

The internal RAM area is used as a stack area, as well as an area to store data. Accordingly, be

sure to set the nesting depth of a subroutine and multiple interrupts’ level not to destroy the necessary

data.

When the internal RAM area is followed by an unused area, do not assign a program to the last 8

bytes of the internal RAM area. (Data is allowed to be assigned there. Also, when the internal RAM

area is followed by the internal ROM area succeedingly, a program is allowed to be assigned there.)

(3)

Internal ROM area

Addresses FFB416 to FFFF16 are the vector addresses for reset and interrupts. (This is called the

interrupt vector table.)

Do not assign a program to the last 8 bytes of the internal ROM area. (Data is allowed to be assigned

there.)

2.4 Memory assignment

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