NXP Semiconductors MPC5644A, Reference Manual, Page: 621 / 1735

Boot Assist Module (BAM)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 621
Chapter 21
Boot Assist Module (BAM)
21.1 Overview
The Boot Assist Module (BAM) is a 4 KB block of read-only memory (ROM) containing the boot
program code for this device.
The BAM program supports four different boot modes:
• Boot from internal Flash
• Serial boot via SCI or CAN interface
• Serial boot via SCI or CAN interface with baud rate detection
• Boot from a memory connected to the External Bus Interface (EBI)
The BAM program is executed by the core just after a device reset. Depending on the boot mode, the
program initializes appropriate minimum device resources to start user code application.
21.2 Features
• Initial core MMU setup with minimum address translation for all internal device resources
• MMU configuration to boot user application, compiled as Power Architecture technology code or
as Freescale VLE code
• Passes control to user application code in the internal flash memory
• Automatic switch to Serial Boot mode if internal flash is blank or invalid
• Serial boot by loading user program via CAN bus or eSCI to the internal SRAM
— User programmable 64-bit password protection
— Optional automatic detection of the host SCI or CAN speed
• Boot from an external memory device, connected to the EBI
• Controls core Watchdog Timer or/and the Software Watchdog Timer (SWT)
21.3 Modes of operation
21.3.1 Normal mode
The BAM program is executed immediately following the negation of reset.
21.3.2 Debug mode
The BAM program is not executed when the device comes out of reset in OnCE debug mode. The user
must provide the required device initialization using the development tool before accessing the device
resources.