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ST7DALI Fiches technique(PDF) 27 Page - STMicroelectronics |
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ST7DALI Fiches technique(HTML) 27 Page - STMicroelectronics |
27 / 141 page ST7DALI 27/141 7.5 RESET SEQUENCE MANAGER (RSM) 7.5.1 Introduction The reset sequence manager includes three RE- SET sources as shown in Figure 14: ■ External RESET source pulse ■ Internal LVD RESET (Low Voltage Detection) ■ Internal WATCHDOG RESET These sources act on the RESET pin and it is al- ways kept low during the delay phase. The RESET service routine vector is fixed at ad- dresses FFFEh-FFFFh in the ST7 memory map. The basic RESET sequence consists of 3 phases as shown in Figure 13: ■ Active Phase depending on the RESET source ■ 256 or 4096 CPU clock cycle delay (see table below) ■ RESET vector fetch The 256 or 4096 CPU clock cycle delay allows the oscillator to stabilise and ensures that recovery has taken place from the Reset state. The shorter or longer clock cycle delay is automatically select- ed depending on the clock source chosen by op- tion byte: The RESET vector fetch phase duration is 2 clock cycles. If the PLL is enabled by option byte, it outputs the clock after an additional delay of tSTARTUP (see Figure 11). Figure 13. RESET Sequence Phases 7.5.2 Asynchronous External RESET pin The RESET pin is both an input and an open-drain output with integrated RON weak pull-up resistor. This pull-up has no fixed value but varies in ac- cordance with the input voltage. It can be pulled low by external circuitry to reset the device. See Electrical Characteristic section for more details. A RESET signal originating from an external source must have a duration of at least th(RSTL)in in order to be recognized (see Figure 15). This de- tection is asynchronous and therefore the MCU can enter reset state even in HALT mode. Figure 14. Reset Block Diagram Clock Source CPU clock cycle delay Internal RC Oscillator 256 External clock (connected to CLKIN pin) 256 External Crystal/Ceramic Oscillator (connected to OSC1/OSC2 pins) 4096 RESET Active Phase INTERNAL RESET 256 or 4096 CLOCK CYCLES FETCH VECTOR RESET RON VDD WATCHDOG RESET LVD RESET INTERNAL RESET PULSE GENERATOR Filter 1 |
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