UPD17708 datasheet(320/356 Pages) NEC

320 / 356 page

320

µPD17704, 17705, 17707, 17708, 17709

21.5 Reset by RESET Pin

The device is reset by the RESET pin in the following cases:

•

To reset the device at voltage higher than power-ON clear voltage

•

External reset input in case of software hang-up

Caution If the device is reset by the RESET pin during program execution, the data in the data memory

may be corrupted.

Therefore, be careful when resetting with the RESET pin.

The reset operation is the same as that performed at power-ON reset.

When a low level is input to the RESET pin, an internal reset signal is generated, the crystal oscillation circuit is

stopped, and the device stops operation.

At this point, the program counter, stack, system registers, and control registers are initialized (for the initial value,

refer to the description of each register).

When the RESET pin is raised next time, the crystal oscillation is started, and the device waits to be released from

the halt wait status by the basic timer 0 carry which has been initialized to a 100-ms cycle. The program starts from

address 0 at the rising edge of the basic timer 0 carry FF setting signal 50 ms after a high level has been input to the

RESET pin.

Because the

µPD17709 has a power-ON reset function, connect the RESET pin to VDD via resistor if the RESET

pin is not used for the above application.

Figure 21-10. Reset Operation by RESET Pin

VDD

RESET

XOUT

BTM0CY flag

setting pulse

5 V

0 V

Device opeation stops

Halt status

50 ms

Oscillation starts

Program starts

from address 0

UPD17708 Datasheet(PDF) 320 Page - NEC