MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 4-13
The fields of the RCHW are shown in Figure 4-3.
Figure 4-3. RCHW Fields
4.4.3.5.2 Invalid RCHW
If the device is configured for a boot from internal flash, a valid boot ID must be read at the lowest address
of one of the six LAS blocks in internal flash memory. If the device is configured for a boot from external
memory, a valid boot ID must be read at 0x00_0000 of CS0. Refer to Chapter 16, “Boot Assist Module
(BAM)” for more information.
0123456789101112131415
WTE PS0 01011010
Boot Identifier = 0x5A
BOOT_BLOCK_ADDRESS + 0x0000_0000
Table 4-9. Internal Boot RCHW Field Descriptions
Bits Name Description
0–4 — Reserved: These bit values are ignored when the halfword is read. Write to 0 for future
compatibility.
5 WTE Watchdog timer enable. This is used to enable or disable the e200z6 watchdog timer
through the BAM program. The configuration of the watchdog timer function is managed
through the timer control register (TCR).
0 BAM does not write the e200z6 timebase registers (TBU and TBL) nor enable the
e200z6 core watchdog timer.
1 BAM writes the e200z6 timebase registers (TBU and TBL) to
0x0000_0000_0000_0000 and enables the e200z6 core watchdog timer with a
time-out period of 3 x 2
17
system clock cycles.
(Example: For 8 MHz crystal 12MHz system clock 32.7mS time-out.
For 20 MHz crystal 30 MHz system clock 13.1mS time-out)
6 PS0 Port size. Defines the width of the data bus connected to the memory on CS
0. After
system reset, CS0 is changed to a 16-bit port by the BAM which fetches the RCHW from
either 16- or 32-bit external memories. Then the BAM reconfigures the EBI either as a
16-bit bus or a 32-bit bus, according to the settings of this bit.
0 32-bit CS0 port size
1 16-bit CS0 port size
Note: Used only in external boot mode. Do not set the port to 32-bits if the device only
has a 16-bit data bus.
7 — Reserved: This bit value is ignored when the halfword is read. Write to 0 for future
compatibility.
8–15 BOOTID
[0:7]
Boot identifier. This field serves two functions. First, it is used to indicate which block in
flash memory contains the boot program. Second, it identifies whether the flash memory
is programmed or invalid. The value of a valid boot identifier is 0x5A (0b01011010). The
BAM program checks the first halfword of each flash memory block starting at block 0
until a valid boot identifier is found. If all blocks in the low address space of the internal
flash are checked and no valid boot identifier is found, then the internal flash is assumed
to be invalid and a CAN/SCI boot is initiated. For an external boot, only block 0 is
checked for a valid boot identifier, and if not found, a CAN/SCI boot is initiated.
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