ST10F276E
Bootstrap loader
Table 28. ST10F276E boot mode selection
P0.5
P0.4
ST10 decoding
1
1
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
1
0
0
0
1
0
Alternate boot mode: Flash mapping depends on signatures integrity check
Reserved
5.2
Standard bootstrap loader
The built-in bootstrap loader of the ST10F276E 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 ST10F276E 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 ST10F276E 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 ST10F276E starts the standard bootstrap loader. This
bootstrap loader is identical to other ST10 devices (Examples: ST10F269, ST10F168). See
Section 5.3 for details.
Valid dominant bit on CAN1 RxD: The ST10F276E starts bootstrapping via CAN1; the
bootstrapping method is new and is described in Section 5.4. 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.
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