Freescale Semiconductor MC9S12ZVHL32, Справочное руководство

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Chapter 21 64 KB Flash Module (S12ZFTMRZ64K2KV2)
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
Freescale Semiconductor 717
The next sections describe:
• How to write the FCLKDIV register that is used to generate a time base (FCLK) derived from
BUSCLK for Flash program and erase command operations
• The command write sequence used to set Flash command parameters and launch execution
• Valid Flash commands available for execution, according to MCU functional mode and MCU
security state.
21.4.5.1 Writing the FCLKDIV Register
Prior to issuing any Flash program or erase command after a reset, the user is required to write the
FCLKDIV register to divide BUSCLK down to a target FCLK of 1 MHz.
Table 21-8 shows recommended
values for the FDIV field based on BUSCLK frequency.
NOTE
Programming or erasing the Flash memory cannot be performed if the bus
clock runs at less than 0.8 MHz. Setting FDIV too high can destroy the Flash
memory due to overstress. Setting FDIV too low can result in incomplete
programming or erasure of the Flash memory cells.
When the FCLKDIV register is written, the FDIVLD bit is set automatically. If the FDIVLD bit is 0, the
FCLKDIV register has not been written since the last reset. If the FCLKDIV register has not been written,
any Flash program or erase command loaded during a command write sequence will not execute and the
ACCERR bit in the FSTAT register will set.
21.4.5.2 Command Write Sequence
The Memory Controller will launch all valid Flash commands entered using a command write sequence.
Before launching a command, the ACCERR and FPVIOL bits in the FSTAT register must be clear (see
Section 21.3.2.7 ) and the CCIF flag should be tested to determine the status of the current command write
sequence. If CCIF is 0, the previous command write sequence is still active, a new command write
sequence cannot be started, and all writes to the FCCOB register are ignored.
21.4.5.2.1 Define FCCOB Contents
The FCCOB parameter fields must be loaded with all required parameters for the Flash command being
executed. The CCOBIX bits in the FCCOBIX register must reflect the amount of words loaded into the
FCCOB registers (see
Section 21.3.2.3 ).
The contents of the FCCOB parameter fields are transferred to the Memory Controller when the user clears
the CCIF command completion flag in the FSTAT register (writing 1 clears the CCIF to 0). The CCIF flag
will remain clear until the Flash command has completed. Upon completion, the Memory Controller will
return CCIF to 1 and the FCCOB register will be used to communicate any results. The flow for a generic
command write sequence is shown in
Figure 21-30 .