UPD17217GT datasheet(51/84 Pages) NEC

51 / 84 page

µPD17215, 17216, 17217, 17218

9.3

Reset by Stack Pointer (Connect RESET and WDOUT pins)

When the value of the stack pointer reaches 6H or 7H during program execution, a low level is output to the WDOUT

pin, and the program counter is reset to 0.

If the nesting level of the interrupt or subroutine call exceeds 5 (stack over flow), or if the return instruction is executed

without correspondence between CALL and return (RET) instructions established, then regardless of a stack level of 0 (stack

underflow), the program can be restarted from address 0H.

Table 9-1 Status of Each Hardware After Reset

Hardware

RESET Input During

RESET Input

Standby Mode

During Operation

Program Counter (PC)

0000H

Port

Input/output

Input

Output latch

Data Memory (RAM)

General-purpose data memory

Retains previous

Undefined

(Except DBF, port register)

status

DBF

0320H

System register (SYSREG)

Retains previous

Undefined

status

Control Register

Refer to Fig. 11-1 Register Files

8-bit Timer

Counter (TMC)

00H

Modulo register (TMM)

FFH

Remote Controller Carrier

NRZ high level period setting modulo register

Retains previous

Undefined

Generator

(NRZHTMM)

status

NRZ low level period setting modulo register

(NRZLTMM)

Basic Interval Timer/Watchdog Timer Counter

00H

10. LOW-VOLTAGE DETECTOR CIRCUIT (CONNECT RESET AND WDOUT PINS)

The low-voltage detector circuit outputs a low level from the WDOUT pin for initialization (reset) to prevent program hang-

up that may take place when the batteries are replaced, if the circuit detects a low voltage.

A drop in the supply voltage is detected if the status of TA = -10 to +85

°C, VDD = 0.8 to 2.2 V lasts for 1 ms or longer.

Note, however, that 1 ms is the guaranteed value and that the microcontroller may be reset even if the above low-voltage

condition lasts for less than 1 ms.

Although the voltage at which the the reset function is effected ranges from 0.8 to 2.2 V, the program counter is prevented

from hang-up even if the supply voltage drops until the reset function is effected, if the instruction execution time is from 8

to 32

µs. Note that some oscillators stop oscillating before the reset function is effected.

The low-voltage detector circuit can be set arbitrarily by the mask option.

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