RM0017 Datasheet, PDF (79/904 Pages) STMicroelectronics – The SPC560Bx and SPC560Cx is a new family

Microcontroller Boot
5
Microcontroller Boot
RM0017
This chapter explains the process of booting the microcontroller. The following entities are
involved in the boot process:
● Boot Assist Module (BAM)
● System Status and Configuration Module (SSCM)
● Flash memory boot sectors (see 28, Flash Memory)
● Memory Management Unit (MMU)
5.1
Boot mechanism
This section describes the configuration required by the user, and the steps performed by
the microcontroller, in order to achieve a successful boot from flash memory or serial
download modes.
There are 2 external pins on the microcontroller that are latched during reset and used to
determine whether the microcontroller will boot from flash memory or attempt a serial
download via FlexCAN or LINFlex (RS232):
● FAB (Force Alternate Boot mode) on pin PA[9]
● ABS (Alternate Boot Select) on pin PA[8]
Table 11 describes the configuration options.
Mode
Table 11. Boot mode selection
FAB pin (PA[9])
Flash memory boot (default mode)
0
Serial boot (LINFlex)
1
Serial boot (FlexCAN)
1
ABS pin (PA[8])
X
0
1
The microcontroller has a weak pull-down on PA[9] and a weak pull-up on PA[8]. This means
that if nothing external is connected to these pins, the microcontroller will enter flash
memory boot mode by default. In order to change the boot behavior, you should use
external pullup or pulldown resistors on PA[9] and PA[8]. If there is any external circuitry
connected to either pin, you must ensure that this does not interfere with the expected value
applied to the pin at reset. Otherwise, the microcontroller may boot into an unexpected
mode after reset.
The SSCM preforms a lot of the automated boot activity including reading the latched value
of the FAB (PA[9]) pin to determine whether to boot from flash memory or serial boot mode.
This is illustrated in Figure 7.
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