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7721 Group User’s Manual

RESET

4–13

4.2 Software reset

When the power source voltage satisfies the microcomputer’s recommended operating conditions, the

microcomputer is reset by writing “1” to the software reset bit (bit 3 at address 5E16). (This is called “

Software reset.”) In this case, the microcomputer initializes pins, CPU, and SFR area just as in the case of

a hardware reset. However, the microcomputer retains the contents of the internal RAM area. (Refer to

“Table 4.1.1” and “Figures 4.1.3 to 4.1.9.”) Figure 4.2.1 shows the structure of the processor mode

After completing initialization, the microcomputer performs “internal processing sequence after reset.” (Refer

to “Figure 4.1.10.”) After that, it executes a program beginning from the address set into the reset vector

addresses (FFFE16 and FFFF16).

Bit

Bit name

Functions

At reset

Software reset bit

Interrupt priority detection

time select bits

Fix this bit to “ 0”

Stack bank select bit

The microcomputer is reset by

writing “1” to this bit.

The value of this bit is “0” at

reading.

0 0 : 7 cycles of

0 1 : 4 cycles of

1 0 : 2 cycles of

1 1 : Do not select.

0 : Bank 016

1 : Bank FF16

b5 b4

Processor mode register 0 (Address 5E16)

: Bits 0 to 2 and bits 4 to 7 are not used for software reset.

Fix this bit to “0”

Nothing is assigned.

This bit is “1” at reading.

Wait bit

0 : Software Wait is inserted when

accessing external area.

1 : No software Wait is inserted

when accessing external area.

Fig. 4.2.1 Structure of processor mode register 0

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