Datasheet

ST10F269 5 - INTERNAL FLASH MEMORY
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5.6 - Bootstrap Loader
The built-in bootstrap loader (BSL) of the
ST10F269 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. 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, to 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 ST10F269 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 ST10F269 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
ST10F269.
Figure 5 : Bootstrap Loader Sequence
RSTIN
TxD0
Internal Boot Memory (BSL) routine 32 Byte user software
2)
3)
RxD0
CSP:IP
4)
6)
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 ST10F269.
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.
1)
5)