Chapter 4 Memory
MC9S08QE128 MCU Series Reference Manual, Rev. 2
Freescale Semiconductor
77
4.6.3
Functional Description
4.6.3.1
Flash Command Operations
Flash command operations are used to execute program, erase, and erase verify algorithms described in
this section. The program and erase algorithms are controlled by the flash memory controller whose time
base, FCLK, is derived from the bus clock via a programmable divider.
The next sections describe:
1. How to write the FCDIV register to set FCLK
2. Command write sequences to program, erase, and erase verify operations on the flash memory
3. Valid flash commands
4. Effects resulting from illegal flash command write sequences or aborting flash operations
4.6.3.1.1
Writing the FCDIV Register
Prior to issuing any flash command after a reset, the user is required to write the FCDIV register to divide
the bus clock down to within the 150 kHz to 200 kHz range. This register can be written only once, so
normally this write is done during reset initialization. FCDIV cannot be written if the access error flag,
FACCERR in FSTAT, is set. The user must ensure that FACCERR is not set before writing to the FCDIV
register. One period of the resulting clock (1/f
FCLK
) is used by the command processor to time program
and erase pulses. An integer number of these timing pulses are used by the command processor to complete
a program or erase command.
shows program and erase times. The bus clock frequency and FCDIV determine the frequency
of FCLK (f
FCLK
). The time for one cycle of FCLK is t
FCLK
= 1/f
FCLK
. The times are shown as a number
of cycles of FCLK and as an absolute time for the case where t
FCLK
= 5
μ
s. Program and erase times
shown include overhead for the command state machine and enabling and disabling of program and erase
voltages.
NOTE
Program and erase command execution time will increase proportionally
with the period of FCLK. Programming or erasing the flash memory with
FCLK < 150 kHz should be avoided. Setting FCDIV to a value such that
FCLK < 150 kHz can destroy the flash memory due to overstress. Setting
FCDIV to a value such that FCLK > 200 kHz can result in incomplete
programming or erasure of the flash memory cells.
Table 4-22. Program and Erase Times
Parameter
Cycles of FCLK
Time if FCLK = 200 kHz
Byte program
9
45
μ
s
Byte program (burst)
4
20
μ
s
1
1
Excluding start/end overhead
Page erase
4000
20 ms
Mass erase
20,000
100 ms
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