HD404374FT datasheet(121/161 Pages) RENESAS

121 / 161 page

HD404374/HD404384/HD404389/HD404082/HD404084 Series

Rev.5.00, Sep.11.2003, page 121 of 161

Notes on PROM Programming

Principles of Programming/Erasure: A memory cell in a ZTAT™ microcomputer is the same as an

EPROM cell; it is programmed by applying a high voltage between its control gate and drain to inject hot

electrons into its floating gate. These electrons are stable, surrounded by an energy barrier formed by an

SiO2 film. The change in threshold voltage of a memory cell with a charged floating gate makes the

corresponding bit appear as 0; a cell whose floating gate is not charged appears as a 1 bit (figure 73).

The charge in a memory cell may decrease with time. This decrease is usually due to one of the following

causes:

• Ultraviolet light excites electrons, allowing them to escape. This effect is the basis of the erasure

principle.

• Heat excites trapped electrons, allowing them to escape.

• High voltages between the control gate and drain may erase electrons.

If the oxide film covering a floating gate is defective, the electron erasure rate will be greater. However,

electron erasure does not often occur because defective devices are detected and removed at the testing

stage.

Control gate

Floating gate

Drain

SiO2

Source

Write (0)

Control gate

Floating gate

Drain

SiO2

Source

Erasure (1)

N+

Figure 73 Cross-Sections of a PROM Cell

PROM Programming: PROM memory cells must be programmed under specific voltage and timing

conditions. The higher the programming voltage VPP and the longer the programming pulse tPW is applied,

the more electrons are injected into the floating gates. However, if VPP exceeds specifications, the pn

junctions may be permanently damaged. Pay particular attention to overshooting in the PROM

programmer. In addition, note that negative voltage noise will produce a parasitic transistor effect that may

reduce breakdown voltages.

The ZTAT™ microcomputer is electrically connected to the PROM programmer by a socket adapter.

Therefore, note the following points:

• Check that the socket adapter is firmly mounted on the PROM programmer.

• Do not touch the socket adapter or the LSI during the programming. Touching them may affect the

quality of the contacts, which will cause programming errors.

HD404374FT Datasheet(PDF) 121 Page - Renesas Technology Corp

HD404374FT Datasheet(HTML) 121 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL