ST10F269 datasheet(109/160 Pages) STMICROELECTRONICS

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ST10F269

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Figure 56 : Synchronous Reset Sequence External Fetch (RSTIN pulse > 1040 TCL)

Note

1) RSTIN rising edge to internal latch of PORT0 is 3 CPU clock cycles (6 TCL) if the PLL is bypassed and the prescaler is on

(fCPU =fXTAL / 2), else it is 4 CPU clock cycles (8 TCL).

2) RSTIN pin is pulled low if bit BDRSTEN (bit 3 of SYSCON register) was previously set by software. Bit BDRSTEN is cleared after

reset.

3) If during the reset condition (RSTIN low), VRPD voltage drops below the threshold voltage (typically 2.5V for 5V operation), the the

ST10 reset circuitry disables the bidirectional reset function and RSTIN pin is no more pulled low.

18.1.3 - Exit of Long Hardware Reset

- If the RPD pin level is low when the RSTIN pin is sampled high, the MCU completes an

asynchronous reset sequence.

If the RPD pin level is high when the RSTIN pin is sampled high, the MCU completes a

synchronous reset sequence.

The system configuration is latched from PORT0 after a duration of 8 TCL / 4 CPU clocks (6 TCL / 3 CPU

clocks if PLL is bypassed) and in case of external fetch, ALE, RD and R/W pins are driven to their inactive

level. The MCU starts program execution from

memory location 00'0000h in code segment 0. This

starting location will typically point to the general initialization routine. Refer to Table 29 for PORT0

latched configuration.

18.2 - Short Hardware Reset

A short hardware reset is a warm reset. It may be generated synchronously to the CPU clock

(synchronous reset).

The short hardware is triggered when RSTIN signal duration is shorter or equal to 1038 TCL, the

RPD pin must be pulled high.

To properly activate the internal reset logic of the MCU, the RSTIN pin must be held low, at least, during

4 TCL (2 periods of CPU clock). The I/O pins are set to high impedance and RSTOUT pin is driven low.

After RSTIN level is detected, a short duration of 12 TCL (6 CPU clocks) maximum elapses, during which

pending internal hold states are cancelled and the current internal access cycle if any is completed.

External bus cycle is aborted. The internal pull-down of RSTIN pin is activated if bit BDRSTEN of

SYSCON register was previously set by software. This bit is always cleared on power-on or after any

reset sequence.

The internal reset sequence starts for 1024 TCL (512 periods of CPU clock).

After that duration the pull-down of RSTIN pin for the bidirectional reset function is released and the

RSTIN pin level is sampled high while RPD level is high.

CPU Clock

RSTIN

RPD

RSTOUT

ALE

PORT0

Latching point of PORT0

for system start-up configuration

6 or 8 TCL1)

4 TCL

12 TCL

min.

max.

1024 TCL

Reset Configuration

If VRPD > 2.5V Asynchronous

200

µA Discharge

Reset is not entered.

Internal reset signal

Internally pulled low

5 TCL

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