MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
4-14 Freescale Semiconductor
If a valid RCHW is not found, a serial boot is initiated. A serial boot does not use a RCHW. The watchdog
timer is enabled. For serial boot entered from a failed external boot, the port size remains configured as 16
bits wide. For serial boot entered from a failed internal boot, the external bus is never configured and
remains in the reset state of GPIO inputs.
4.4.3.5.3 Reset Configuration Halfword Source
The reset configuration halfword (RCHW) specifies a minimal MCU configuration after reset. The RCHW
also contains bits that control the BAM program flow. See Section 16.3.2.1.1, “Finding Reset
Configuration Half Word” for information on the BAM using the RCHW. The RCHW is read and applied
each time the BAM program executes, which is for every power-on, external, or internal reset event. The
only exception to this is the software external reset. See Section 4.4.3.5, “Reset Configuration Half Word,”
for detailed descriptions of the bits in the RCHW. The RCHW is read from one of the following locations:
• The lowest address (0x00_0000) of an external memory device, enabled by chip select CS0 using
either a 16- or 32-bit data bus
• The lowest address of one of the six low address space (LAS) blocks in the internal flash memory.
(2 x 16K; 2 x 48K; 2 x 64K)
At the negation of the RSTOUT pin, the BOOTCFG field in the RSR has been updated. If BOOTCFG0 is
asserted, then the BAM program reads the RCHW from address 0x0000_0000 in the external memory
connected to CS0 (the BAM first configures the MMU and CS0 such that address 0x0000_0000 is
translated to 0x2000_0000 and then directed to CS0). When BOOTCFG0 is asserted, BOOTCFG1
determines whether external arbitration must be enabled to fetch the RCHW.
If BOOTCFG0 and BOOTCFG1 are negated at the negation of the RSTOUT pin, then the BAM program
attempts to read the RCHW from the first address of each of the 6 blocks in the low address space (LAS)
of internal flash. Table 4-10 shows the LAS addresses.
If the RCHW stored in either internal or external flash is invalid (boot identifier field of RCHW is not
0x5A), or if BOOTCFG0 is negated and BOOTCFG1 is asserted at the negation of the RSTOUT
pin, then
RCHW is not applicable, and serial boot mode is performed. Table 4-11 summarizes the RCHW location
options.
Table 4-10. LAS Block Memory Addresses
Block Address
0 0x0000_0000
1 0x0000_4000
2 0x0001_0000
3 0x0001_C000
4 0x0002_0000
5 0x0003_0000
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