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RESET

7906 Group User’s Manual Rev.2.0

3-2

There are 3 ways to reset the microcomputer:

Hardware reset : Apply “L” level of voltage to pin RESET while the power source voltage (Vcc) meets

the recommended operating conditions.

Software reset : Write “1” to the software reset bit (bit 6 at address 5E16) while the power source

voltage (Vcc) meets the recommended operating conditions.

Power-on reset : After power-on, raise the voltage level at pin Vcc to the level, which meets the

recommend operating conditions, with “L” level of voltage applied to pin RESET.

3.1 Reset operation

Operations of hardware, software, and power-on reset are described below.

3.1.1 Hardware reset

Figure 3.1.1 shows an example of hardware reset timing.

Fig. 3.1.1 Example of hardware reset timing

The following explains how the microcomputer operates in the above periods, ➀ to ➃.

➀ After applying “L” level of voltage to pin RESET, the microcomputer initializes pins within a period of several

ten cycles of fsys. (Refer to section “3.2 Pin state.”)

➁ The microcomputer initializes the central processing unit (CPU) and SFR area in the following periods.

(Refer to section “3.3 State of internal area.”)

• While pin RESET is at “L” level.

• In the period of 8 to 9 cycles of fsys after pin RESET goes from “L” to “H.”

➂ After ➁, the microcomputer performs “Internal processing sequence after reset.” (Refer to section “3.4

Internal processing sequence after reset.”)

➃ The microcomputer executes a program beginning with the address which has been set into the reset

vector addresses (addresses FFFE16 and FFFF16).

RESET

µs or more

8 to 9 cycles of fsys

Internal processing

sequence after

reset

Program is executed.

(Note)

➀

➁

➂

➃

Note: The above is applied when the oscillator is stably oscillating or when an

external clock is stably input from pin XIN. When the oscillator is not stably

oscillating (including the case at the stop mode’s termination; refer to section

“15.3 Stop mode.”), apply “L” level of voltage for 10

µs or more after the

oscillation becomes stable.

3.1 Reset operation

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