AN2400 Freescale Semiconductor / Motorola, AN2400 Datasheet - Page 3

• Manufacturer Part Number: AN2400
• Description: HCS12 NVM Guidelines
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
AN2400/D
Split-Gate Flash Memory
Bitlines
Wordline
Source
Figure 2. One quarter of a Split-Gate Flash Word
To program a word, a high positive voltage (>>VDD) is applied to the cell
sources. The control gates have ~VDD applied through the wordline. Cells that
are to be programmed to ‘0’ have a low voltage (~0V) applied to the drain
through the bitlines, as depicted in
Figure
3. A high electric field is created at
the gap between the floating gate and the control gate which causes some
electrons in the source-drain channel to be injected into the floating gate,
leaving the floating gate with a slightly negative charge. Cells that are to remain
in the erased state have a voltage (~VDD) applied to the drain through the
bitline. This changes the electric field and no electrons are injected into the
floating gate. When the high voltage is switched off, the floating gate retains its
charge indefinitely. Programming is a quick process, taking only a few
microseconds per word.
0V
VDD
VDD
0V
VDD
>>VDD
Figure 3. Programming a ‘0101’ pattern into Split-Gate Flash
To read a word, the cells sources are connected to VSS (0V) and ~VDD is
applied to the control gates through the wordline, as shown in
Figure
4. Current
flows through the drain to the source only if the control gate is positively
charged (erased state), so the bitline current is sensed to determine whether
the cell should read as a ‘1’ (erased) or ‘0’ (programmed).
MOTOROLA
HCS12 NVM Guidelines
3
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