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Section 6 ROM
Rev. 6.00 Sep 12, 2006 page 111 of 526
REJ09B0326-0600
6.4
Flash Memory Overview
6.4.1
Principle of Flash Memory Operation
Table 6.5 illustrates the principle of operation of the on-chip flash memory in the H8/3644F,
H8/3643F, and H8/3642AF.
Like EPROM, flash memory is programmed by applying a high gate-to-drain voltage that draws
hot electrons generated in the vicinity of the drain into a floating gate. The threshold voltage of a
programmed memory cell is therefore higher than that of an erased cell. Cells are erased by
grounding the gate and applying a high voltage to the source, causing the electrons stored in the
floating gate to tunnel out. After erasure, the threshold voltage drops. A memory cell is read like
an EPROM cell, by driving the gate to a high level and detecting the drain current, which depends
on the threshold voltage. Erasing must be done carefully, because if a memory cell is overerased,
its threshold voltage may become negative, causing the cell to operate incorrectly.
Section 6.7.6, Erase Flowcharts and Sample Programs, shows optimal erase control flowcharts and
sample programs.
Table 6.5
Principle of Memory Cell Operation
Program
Erase
Read
Memory
cell
Vg = V
PP
Vd
Vs = V
PP
Open
Vg = V
CC
Vd
Memory
array
V
PP
Vd
0 V
0 V
0 V
0 V
Open
V
PP
Open
0 V
V
CC
Vd
0 V
0 V
0 V
Summary of Contents for F-ZTAT H8/3642A Series
Page 6: ...Rev 6 00 Sep 12 2006 page iv of xx ...
Page 8: ...Rev 6 00 Sep 12 2006 page vi of xx ...
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Page 124: ...Section 5 Power Down Modes Rev 6 00 Sep 12 2006 page 102 of 526 REJ09B0326 0600 ...
Page 188: ...Section 6 ROM Rev 6 00 Sep 12 2006 page 166 of 526 REJ09B0326 0600 ...
Page 190: ...Section 7 RAM Rev 6 00 Sep 12 2006 page 168 of 526 REJ09B0326 0600 ...
Page 298: ...Section 9 Timers Rev 6 00 Sep 12 2006 page 276 of 526 REJ09B0326 0600 ...
Page 378: ...Section 12 A D Converter Rev 6 00 Sep 12 2006 page 356 of 526 REJ09B0326 0600 ...
Page 446: ...Section 13 Electrical Characteristics Rev 6 00 Sep 12 2006 page 424 of 526 REJ09B0326 0600 ...