AN3995 datasheet(7/49 Pages) STMICROELECTRONICS

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AN3995

Microcontroller boot

Doc ID 022384 Rev 2

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Microcontroller boot

This chapter describes the configuration required by the user, and the steps performed by

the microcontroller(b) and in particular, by the SSCM (System Status and Configuration

Module), in order to achieve a successful boot from Flash memory.

For further information, look at SPC564Bxx and SPC56ECxx Reference Manual (see

Section C.1: Reference document).

2.1

Boot mechanism

SPC564Bxx and SPC56ECxx family (as other SPC56xx devices), has two hardware boot

configuration pins, FAB (Force Alternate Boot mode) and ABS (Alternate Boot Select).

These 2 external pins on the microcontroller are latched during reset and used by the SSCM

to determine whether the microcontroller boots from Flash memory or attempts a serial

download via FlexCAN or LINFlex (RS232) (see Table 1).

In this application note, the focus is on the default operating mode: the Flash boot mode.

When the device is powered on, the SSCM (System Status Configuration Module) searches

the pre-determined locations in Flash for a valid RCHW (Reset Configuration Half Word)

(see Section 2.1.1: Bootable sectors and RCHW).

●

If a valid BOOT_ID is found, the SSCM reads the VLE bit and the boot vector address

(as well as the CSE block size).

●

If a valid BOOT_ID is not found, the SSCM starts the process of putting the

microcontroller (e200z4d) into static mode(c). See SPC564Bxx and SPC56ECxx family

Reference Manual for detailed information (see Section C.1: Reference document).

Note:

The static mode differs from safe mode. Static mode is a non-operational mode which can

only be entered via the BAM (Boot Assist Module).

The booting mechanism has an impact only on the e200z4d core.

Table 1.

Boot mode selection

Mode

FAB pin (PA[9])

ABS pin (PA[8])

Flash Boot (Default Mode)

–

Serial Boot (LINFlex)

Serial Boot (FlexCAN)

Static Mode Sequence:

1. The SSCM creates a 4 KB MMU page at the start of the BAM with the VLE bit set (the BAM is VLE code).

2. The SSCM then sets the CPU core (e200z4d) instruction pointer to the BAM address and the core starts to

execute the code to enter static mode as follows:

- the Software Watchdog Timer (SWT) is enabled;

- the core executes the "wait" instruction which halts the core.

After the microcontroller enters static mode, the SWT periodically resets the core (approximately every 10 ms)

to re-attempt a boot from Flash memory.

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