ST7L09 datasheet(26/104 Pages) STMICROELECTRONICS

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ST7L05, ST7L09

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SUPPLY, RESET AND CLOCK MANAGEMENT (Cont’d)

7.4 RESET SEQUENCE MANAGER (RSM)

7.4.1 Introduction

The reset sequence manager includes two RE-

SET sources as shown in Figure 14:

■ External RESET source pulse

■ Internal WATCHDOG RESET

Note: A reset can also be triggered following the

detection of an illegal opcode or prebyte code. Re-

fer to Section 12.2.1 on page 70 for further details.

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 three

phases as shown in Figure 13:

■ Active Phase depending on the RESET source

■ 256 CPU clock cycle delay

■ RESET vector fetch

Caution: When the ST7 is unprogrammed or fully

erased, the Flash is blank and the RESET vector

is not programmed. For this reason, it is recom-

mended to keep the RESET pin in low state until

programming mode is entered, in order to avoid-

unwanted behavior.

The 256 CPU clock cycle delay allows the oscilla-

tor to stabilize and ensures that recovery has tak-

en place from the Reset state.

The RESET vector fetch phase duration is two

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

Figure 14. ST7L0x Reset Block Diagram

RESET

Active Phase

INTERNAL RESET

256 CLOCK CYCLES

FETCH

VECTOR

RESET

RON

VDD

INTERNAL

RESET

PULSE

GENERATOR

FILTER

Note 1: See “Illegal Opcode Reset” on page 70. for more details on illegal opcode reset conditions.

WATCHDOG RESET

ILLEGAL OPCODE RESET1)

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