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5.3 Notes on the External Flash Memory
The external flash memory, which is produced by Texas Instruments, has to be con-
figured before you can read from it. This procedure is described in the data sheet of
the flash memory.
Table 5-2 External flash memory at different clock rates
The flash memory only works correctly at a bus clock rate of 33 MHz or less. The
resulting variants for the EVB555 are shown in Table 5-2.
5.4 Booting on the EVB555
To be able to start a program without a BDM debugger, it is necessary to boot from
non-volatile memory (i.e., from flash memory). The mode can be set via the reset con-
figuration word (see Section 4.6.2.). There are a few points about the EVB555 that
should be observed.
The external flash memory cannot be used for booting since it does not provide a
mechanism for saving its start-up configuration. It has to be configured before you can
read from it.
Booting from the internal flash of the MPC555 is supported by the evaluation board.
Earlier versions of the MPC555 are not, however, capable of booting from the internal
flash at an internal clock rate of 20 MHz. The standard clock rate is 20 MHz, which is
generated by multiplying the crystal frequency (4 MHz) with the mode clock configura-
tion factor 5.
You can solve this problem by exchanging the external crystal. It is recommended that
]SY VITPEGI XLI 1,^ GV]WXEP F] E 1,^ X]TI ERH STIVEXI XLI 400 SJ XLI
14' MR QSHI -R XLEX GEWI ]SY [MPP IRH YT [MXL E 1,^ VEXI 8LI ZEPYI
SJ XLI QSHI GPSGO has to be changed to "011" for this purpose 7IGXMSR ). This
mode is within the PLL specification and even earlier versions of the MPC555 should
boot reliably from internal flash memory. If you want to operate the board in this way
long-term, you should reduce the capacitor at the XFC output (C201) to 560 pF.
MOTOROLA
5-26
Internal clock
Bus clock
32MHz
32MHz
40MHz
20MHz
40MHz
40MHz
External flash usable
Yes
Yes
No
EVB555
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