ST10F276 datasheet(47/229 Pages) STMICROELECTRONICS

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ST10F276

Bootstrap loader

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5.2

Standard bootstrap loader

The built-in bootstrap loader of the ST10F276 provides a mechanism to load the startup

program, which is executed after reset, via the serial interface. In this case no external

(ROM) memory or an internal ROM is required for the initialization code starting at location

00’0000H. The bootstrap loader moves code/data into the IRAM but it is also possible to

transfer data via the serial interface into an external RAM using a second level loader

routine. ROM memory (internal or external) is not necessary. However, it may be used to

provide lookup tables or may provide “core-code”, that is, a set of general purpose

subroutines, such as for I/O operations, number crunching or system initialization.

The Bootstrap Loader can load

●

the complete application software into ROMless systems,

●

temporary software into complete systems for testing or calibration,

●

a programming routine for Flash devices.

The BSL mechanism may be used for standard system start-up as well as for only special

occasions like system maintenance (firmware update) or end-of-line programming or

testing.

5.2.1

Entering the standard bootstrap loader

As with the old ST10 bootstrap mode, the ST10F276 enters BSL mode if pin P0L.4 is

sampled low at the end of a hardware reset. In this case, the built-in bootstrap loader is

activated independently of the selected bus mode. The bootstrap loader code is stored in a

special Test-Flash; no part of the standard Flash memory area is required for this.

After entering BSL mode and the respective initialization, the ST10F276 scans the RxD0

line and the CAN1_RxD line to receive either a valid dominant bit from the CAN interface or

a start condition from the UART line.

Start condition on UART RxD: The ST10F276 starts the standard bootstrap loader. This

bootstrap loader is identical to other ST10 devices (Examples: ST10F269, ST10F168). See

paragraph 5.3 for details.

Valid dominant bit on CAN1 RxD: The ST10F276 starts bootstrapping via CAN1; the

bootstrapping method is new and is described in the next paragraph 5.4. The following

Figure 5 shows the program flow of the new bootstrap loader. It clearly illustrates how the

new functionalities are implemented:

●

UART: UART has priority over CAN after a falling edge on CAN1_RxD until the first

valid rising edge on CAN1_RxD;

●

CAN: Pulses on CAN1_RxD shorter than 20*CPU-cycles are filtered.

Table 28.

ST10F276 boot mode selection

P0.5

P0.4

ST10 decoding

User mode: User Flash mapped at 00’0000h

Standard bootstrap loader: User Flash mapped from 00’0000h; code fetches

redirected to Test-Flash at 00’0000h

Alternate boot mode: Flash mapping depends on signatures integrity check

Reserved

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