ST10F272Z2Q3 datasheet(99/189 Pages) STMICROELECTRONICS

99 / 189 page

ST10F272Z2

System reset

99/189

Figure 29.

SW / WDT bidirectional RESET (EA=0) followed by a HW RESET

20.7

Reset circuitry

Internal reset circuitry is described in Figure 32. The RSTIN pin provides an internal pull-up

resistor of 50 k

Ω to 250 kΩ (The minimum reset time must be calculated using the lowest

value).

It also provides a programmable (BDRSTEN bit of SYSCON register) pull-down to output

internal reset state signal (synchronous reset, watchdog timer reset or software reset).

This bidirectional reset function is useful in applications where external devices require a

reset signal but cannot be connected to RSTOUT pin.

This is the case of an external memory running codes before EINIT (end of initialization)

instruction is executed. RSTOUT pin is pulled high only when EINIT is executed.

The RPD pin provides an internal weak pull-down resistor which discharges external

capacitor at a typical rate of 200

µA. If bit PWDCFG of SYSCON register is set, an internal

pull-up resistor is activated at the end of the reset sequence. This pull-up will charge any

capacitor connected on RPD pin.

The simplest way to reset the ST10F272Z2 is to insert a capacitor C1 between RSTIN pin

and VSS, and a capacitor between RPD pin and VSS (C0) with a pull-up resistor R0 between

RPD pin and VDD. The input RSTIN provides an internal pull-up device equalling a resistor of

50 k

Ω to 250 kΩ (the minimum reset time must be determined by the lowest value). Select

C1 that produce a sufficient discharge time to permit the internal or external oscillator and /

or internal PLL and the on-chip voltage regulator to stabilize.

P0[15:13]

not transparent

RSTF

P0[12:8]

transparent

not t.

P0[1:0]

not t.

not transparent

RST

1024 TCL

RSTOUT

At this time RSTF is sampled LOW

so HW Reset is entered

(After Filter)

RSTIN

≤ 500 ns

≥ 50 ns

ALE

8 TCL

≤ 500 ns

≥ 50 ns

P0[7:2]

not transparent

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