Information

The 'user' and 'factory' levels become, in effect, a minimum safety margin; i.e. if the reads
pass at the tighter tolerances of the 'user' and 'factory' margins, then the 'normal' reads
have at least this much safety margin before they experience data loss.
The 'user' margin is a small delta to the normal read reference level. 'User' margin levels
can be employed to check that flash memory contents have adequate margin for normal
level read operations. If unexpected read results are encountered when checking flash
memory contents at the 'user' margin levels, loss of information might soon occur during
'normal' readout.
The 'factory' margin is a bigger deviation from the norm, a more stringent read criteria
that should only be attempted immediately (or very soon) after completion of an erase or
program command, early in the cycling life. 'Factory' margin levels can be used to check
that flash memory contents have adequate margin for long-term data retention at the
normal level setting. If unexpected results are encountered when checking flash memory
contents at 'factory' margin levels, the flash memory contents should be erased and
reprogrammed.
CAUTION
Factory margin levels must only be used during verify of the
initial factory programming.
28.4.11 Flash Command Description
This section describes all flash commands that can be launched by a command write
sequence. The flash memory module sets the FSTAT[ACCERR] bit and aborts the
command execution if any of the following illegal conditions occur:
• There is an unrecognized command code in the FCCOB FCMD field.
• There is an error in a FCCOB field for the specific commands. Refer to the error
handling table provided for each command.
Ensure that the ACCERR and FPVIOL bits in the FSTAT register are cleared prior to
starting the command write sequence. As described in Launch the Command by Clearing
CCIF, a new command cannot be launched while these error flags are set.
Do not attempt to read a flash block while the flash memory module is running a
command (CCIF = 0) on that same block. The flash memory module may return invalid
data to the MCU with the collision error flag (FSTAT[RDCOLERR]) set.
When required by the command, address bit 23 selects between:
Flash Operation in Low-Power Modes
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
534 Freescale Semiconductor, Inc.