User Manual
305
Rev. 1.1
2019-03-18
TLE984xQX
Microcontroller with LIN and Power Switches for Automotive Applications
NVM Module (Flash Memory)
12.1
Definitions
This section defines the nomenclature and some abbreviations. The used flash memory is a non-volatile
memory (“NVM”) based on a floating gate one-transistor cell. It is called “non-volatile” because the memory
content is kept when the memory power supply is shut off.
12.1.1
General Definitions
Logical and Physical States
Erasing
The erased state of a cell is ´1´. Forcing an NVM cell to this state is called erasing. Erasing is possible with a
granularity of a page (see below).
Writing
The written state of a cell is ´0´. Forcing an NVM cell to this state is called writing. Each bit can be individually
written.
Programming
The combination of erasing and writing is called ‘programming’. Programming often means also writing a
previously erased page.
The wording ‘write’ or ‘writing’ are also used for accessing special function registers and the assembly buffer.
The meaning depends therefore on the context.
The above listed processes have certain limitations:
Retention: This is the time during which the data of a flash cell can be read reliably. The retention time is a
statistical figure that depends on the operating conditions of the flash array (temperature profile) and the
accesses to the flash array. With an increasing number of program/erase cycles (see endurance) the retention
is lowered. Drain and gate disturbs decrease data retention as well.
Endurance: As described above, the data retention is reduced with an increasing number of program/erase
cycles. A flash cell incurs one cycle whenever its page or sector is erased. This number is called “endurance”.
As said for the retention, it is a statistical figure that depend on operating conditions and the use of the flash
cells and on the required quality level.
Drain Disturb: Because of using a so called “one-transistor” flash cell each program access disturbs all pages
of the same sector slightly. Over long these “drain disturbs” make 0 and 1 values indistinguishable and thus
provoke read errors. This effect is again interrelated with the retention. A cell that incurred a high number of
drain disturbs will have a lower retention. The physical sectors of the flash array are isolated from each other.
So pages of a different sector do not incur a drain disturb. this effect must be therefore considered when the
page erase feature is used or when re-programming an ready programmed page (implicitly causing an erase
of the page before writing the new data).
Data Portions
