ST10F269Z2QX datasheet(30/161 Pages) STMICROELECTRONICS

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ST10F269Z2Qx

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5.6 - Bootstrap Loader

The

built-in

bootstrap

loader

(BSL)

the

ST10F269Z2Qx provides a mechanism to load

the startup program through the serial interface

after reset. In this case, no external memory or

internal

Flash

memory

required

for

the

initialization code starting at location 00’0000h

(see Figure 5).

The bootstrap loader moves code/data into the

internal RAM, but can also transfer data via the

serial interface into an external RAM using a

second level loader routine. Flash Memory

(internal or external) is not necessary, but it may

be used to provide lookup tables or “core-code”

like a set of general purpose subroutines for I/O

operations,

number

crunching,

system

initialization, etc.

The bootstrap loader can be used to load the

complete

application

software

into

ROMless

systems,

load

temporary

software

into

complete systems for testing or calibration, or to

load a programming routine for Flash devices.

The BSL mechanism can be used for standard

system startup as well as for special occasions

like system maintenance (firmer update) or

end-of-line programming or testing.

5.6.1 - Entering the Bootstrap Loader

The ST10F269Z2Qx enters BSL mode when pin

P0L.4 is sampled low at the end of a hardware

reset. In this case the built-in bootstrap loader is

activated independent of the selected bus mode.

The bootstrap loader code is stored in a special

Boot-ROM. No part of the standard mask Memory

or Flash Memory area is required for this.

After entering BSL mode and the respective

initialization the ST10F269Z2Qx scans the RXD0

line to receive a zero Byte, one start bit, eight ‘0’

data bits and one stop bit.

From the duration of this zero Byte it calculates

the corresponding Baud rate factor with respect to

the current CPU clock, initializes the serial

interface ASC0 accordingly and switches pin

TxD0 to output.

Using this Baud rate, an identification Byte is

returned to the host that provides the loaded data.

This identification Byte identifies the device to

be booted. The identification byte is D5h for

ST10F269Z2Qx.

Figure 5 : Bootstrap Loader Sequence

RSTIN

TxD0

Internal Boot Memory (BSL) routine

32 Byte user software

RxD0

CSP:IP

P0L.4

1) BSL initialization time

2) Zero Byte (1 start bit, eight ‘0’ data bits, 1 stop bit), sent by host.

3) Identification Byte (D5h), sent by ST10F269Z2Qx.

4) 32 Bytes of code / data, sent by host.

5) Caution: TxD0 is only driven a certain time after reception of the zero Byte.

6) Internal Boot ROM.

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