
Chapter 23 1024 KByte Flash Module (S12XFTM1024K5V2)
MC9S12XE-Family Reference Manual Rev. 1.07
Freescale Semiconductor
875
23.4
Functional Description
23.4.1
Flash Command Operations
Flash commands operations are used to modify Flash memory contents or configure module resources for
EEE operation.
The next sections describe:
1.
How to write the FCLKDIV register that is used to generate a time base (FCLK) derived from the
oscillator clock (XTAL) for Flash program and erase command operations
2.
The command write sequence used to set Flash command parameters and launch execution
3.
Valid Flash commands available for execution
23.4.1.1
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 the oscillator clock (XTAL) down to a target FCLK of 1 MHz (range of 800
kHz to 1.05 MHz).
Table 23-8
shows recommended values for FDIV[6:0] based on XTAL frequency.
NOTE
Because of the impact of clock synchronization, programming or erasing
the Flash memory cannot be performed if the bus clock runs at less than 1
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.
If 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,
the Flash program or erase command loaded during a command write sequence will not execute and the
ACCERR bit in the FSTAT register will set.