ST10F280 datasheet(34/186 Pages) STMICROELECTRONICS

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ST10F280

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5.6 - Bootstrap Loader

The

built-in

bootstrap

loader

(BSL)

the

ST10F280 provides a mechanism to load the

startup program through the serial interface after

reset. In this case, no external memory or internal

Flash memory is 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.

ROM

Memory

(internal or external) is not necessary, but it

may be

used

provide

lookup

tables

“core-code”

set

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 ST10F280 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 ST10F280 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.

Identification

byte

D5h

for

the

ST10F280.

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 ST10F280.

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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