MC9S12E256 Datasheet, PDF (578/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Appendix A Electrical Characteristics
A.4 Flash NVM
A.4.1 NVM Timing
The time base for all NVM program or erase operations is derived from the oscillator. A minimum
oscillator frequency f_NVMOSC is required for performing program or erase operations. The NVM modules
do not have any means to monitor the frequency and will not prevent program or erase operation at
frequencies above or below the specified minimum. Attempting to program or erase the NVM modules at
a lower frequency a full program or erase transition is not assured.
The Flash program and erase operations are timed using a clock derived from the oscillator using the
FCLKDIV register. The frequency of this clock must be set within the limits specified as f_NVMOP.
The minimum program and erase times shown in Table A-14 are calculated for maximum f_NVMOP and
maximum f_bus. The maximum times are calculated for minimum f_NVMOP and a f_bus of 2MHz.
A.4.1.1 Single Word Programming
The programming time for single word programming is dependent on the bus frequency as a well as on the
frequency f¨_NVMOP and can be calculated according to the following formula.
tswpgm
=
9
⋅
-----------1-------------
fNVMOP
+
25
⋅
-----1------
fbus
A.4.1.2 Row Programming
Flash programming where up to 64 words in a row can be programmed consecutively by keeping the
command pipeline filled. The time to program a consecutive word can be calculated as:
tbwpgm
=
4
⋅
------------1------------
fNVMOP
+
9
⋅
-----1------
fbus
The time to program a whole row is:
tbrpgm = tswpgm + 63 ⋅ tbwpgm
Row programming is more than 2 times faster than single word programming.
A.4.1.3 Sector Erase
Erasing a 1024 byte Flash sector takes:
tera
≈
4000
⋅
-----------1-------------
fNVMOP
The setup times can be ignored for this operation.
MC9S12E256 Data Sheet, Rev. 1.08
578
Freescale Semiconductor