PXS20RM Datasheet, PDF (129/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Chapter 5
Device Boot Modes
Device Boot Modes
5.1 Boot mode functionality
The device supports the following boot modes:
• Single Chip (SC) — the device will boot from the first bootable section of the flash memory main
array
• Serial Boot (SBL) — the device will download boot code from either SCI or CAN interface and
then execute it
If booting is not possible with the selected configuration (e.g. if no Boot ID is found in the selected boot
location) then the device will enter static mode (see Section 5.4.6, Static Mode).
5.2 Hardware configuration
The device will detect the boot mode based on external pins and device status. The following sequence
applies:
• If the FAB (Force Alternate Boot Mode) pin is set to boot in serial mode, the device can be forced
into an Alternate Boot Loader Mode. The type of alternate boot mode is selected according to the
ABS (Alternate Boot Selector) pins (see Table 5-1). For details of the serial boot modes please see
Chapter 8, Boot Assist Module (BAM).
• If the device identifies a flash memory sector with a valid boot signature, it will boot from the
lowest sector. (See Figure 5-1.)
• If none of the flash memory sectors contains a valid boot signature, the device will go into static
mode.
Table 5-1. Hardware configuration
FAB
ABS Standby-RAMB
2,0
oot Flag
Boot ID
1
00
0
—
1
01
0
—
0
—
0
valid
0
—
0
not found
Boot Mode
Serial Boot SCI
Serial Boot CAN
SC (Single Chip)
Static Mode
5.2.1 Single chip boot mode
The SSCM performs a sequential search of each bootable sector (starting at sector 0) for a valid BOOT_ID
within the RCHW. If a valid BOOT_ID is found in the RCHW of such a sector , the SSCM reads the VLE
bit and the boot vector address. If a valid BOOT_ID is not found, the microcontroller is put into static
mode.
In order for the e200z4d core to be able to access its program space memory , a valid MMU TLB entry has
to be created. The SSCM does this automatically by reading the reset vector (the word after the RCHW)
and modifying TLB entry 0 to create a 4 KB page containing the reset vector address. The corresponding
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
5-1