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HA16117F

CMOS Watchdog Timer

Renesas Electronics 

HA16117F Series

Setting of RES Timing and Watchdog Frequency Range

Different MPUs have different RES timing requirements. The minimum reset time (tON) required at power-on (rise of

VCC) is 20 ms for some MPUs and 100 ms for others.

RES timing waveform parameters must be selected according to the MPU. With the HA16117F the timing of the RES

output and the watchdog frequency range can both be set by external constants (CF, CR, and K).

Parameters

Item

Symbol

CR (pin 4)

CF (pin 3)

Power-on reset time

tON

Reset-clock off time

tOFF

S *2

Reset low time

tRL

Reset high time

tRH

Watchdog frequency high

fH

Watchdog frequency low

fL

Notes: 1. K = R2 / (R1 + R2)

2. Variability of tOFF increases with increasing CF. The variability ∆tOFF is approximately

3.3 (MΩ) × CF (µF), so CF ≤ 0.01 (µF) is recommended.

3. External constants should be selected with reference to the formulas in tables 1 and 2.

K (pin 8) *1

Table 1

tON (ms)

tOFF (ms)

tRL (ms)

tRH (ms)

tSL (ms)

Calculation of RES Output Timing

Item

Formula

400 (Ω) × CR (µF)

1.99 × tRH (ms)

0.5 × tON (ms)

K

×

31

1.6

(µA)

(V)

− 15.8

(µA)

×

CR

(µF)

×

103

≈ tOFF (ms)

Notes

tON and tOFF can be set independently

tRL and tRH can be set independently

Table 2

fH (MHz)

fL (Hz)

Calculation of Watchdog Frequency Range

Item

Formula

1

500 (Ω) × CF (µF)

×

tRH (ms) − tRL (ms)

tRH (ms) + tRL (ms)

1

1.7 (MΩ) × CF (µF)

×

tRL (ms)

tRH (ms) + tRL (ms)

or

1

tOFF (ms)

× 103

Whichever is larger

Rev.3.00 Jun 15, 2005 page 16 of 30

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