JPH042480Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention is a programmable read-only memory (PROM) that has a dedicated program terminal (terminal) to prevent erroneous writing.
Regarding.

[Prior art]

PROM is a ROM in which information can be rewritten and is an important component of information processing devices such as microcomputers.

PROMs often have dedicated terminals, and when writing data to such PROMs, the terminals are made active (low level) as shown in Figure 1, and the data programmed at that time is
Written into PROM. In the figure, it is a chip enable signal.

PROM with necessary data already written
Also, due to circuit malfunction, previously programmed data may be rewritten by applying a signal like that shown in Figure 1 to the PROM. (In a normal PROM, the data does not change from 0 to 1, but it can be rewritten from 1 to 0.) PROM's original feature is that the data can be rewritten. In many cases, stable data that does not need to be rewritten is written and used. However, such usage has the disadvantage that there is a high risk of erroneous writing as described above.

[Purpose of invention]

The present invention aims to eliminate the drawbacks of the prior art by providing a PROM that prevents erroneous writing by having a structure that allows the signal path from the terminal to the internal circuit to be cut off from the outside. .

[Structure of the idea]

The PROM of this invention has dedicated terminals.
The PROM has a structure in which control wiring is inserted and connected in series at a predetermined position on a signal path from the terminal to the internal circuit, and the control wiring can be cut off from the outside.

[Explanation of Examples]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2a is a plan view showing the essential parts of the first embodiment of the present invention, and FIG. 2b is a partially enlarged plan view of the package near the terminal with the lid removed.

This embodiment has a dedicated terminal 2.
In the PROM 1, thin wires 5 made of aluminum or gold, for example, are inserted and connected in series as control wiring at predetermined positions of the wiring 4 as a signal path from the terminal 2 to the chip 3 where an internal circuit is formed, and the connection points are This is achieved by providing a window 6 for cutting thin wire. Note that 7 is a window for memory erasure.

In the PROM of this embodiment, after writing the necessary data, the thin wire 5 visible through the thin wire cutting window 6 is cut with, for example, a cutter knife. In this way, the signal path from the terminal is cut off, so
There is no risk of erroneous writing as in the past.

In this case, the window frame for thin wire cutting is formed to maintain airtightness, and the window is covered with a thin sheet of synthetic resin, for example, so that it can be broken by external pressure, or in some cases, this cover may not be provided. .

FIG. 3 is a circuit diagram showing the main parts of a second embodiment of the present invention. A fuse 14 is installed as a control wiring in the middle of the wiring 13 between the internal circuit 11 and the terminal 12.
is provided, one end of the fuse 14 is connected to the terminal 12,
This embodiment works by connecting the other ends to the know connection (NC) terminals 15 (see FIG. 2a) of the PROM.

In this embodiment, after writing the necessary data, a voltage necessary to blow out the fuse 14 is applied between the terminal 12 and the NC terminal 15 to blow out the fuse 14. Thus, in the PROM of this embodiment, there is no risk of erroneous data writing as in the prior art.

Note that this second embodiment has an NC terminal.
Although it can only be applied to PROMs, many PROMs with terminals also have NC terminals. Furthermore, in the case of this embodiment, unlike the first embodiment shown in FIG.
PROM is obtained.

Although two embodiments have been described above, it is clear that the PROM of the present invention only needs to have a structure that allows the signal path from the terminal to the internal circuit to be cut off from the outside.

[Effect of idea]

As explained in detail above, the PROM of the present invention
Since it has a structure in which the signal path from the terminal to the internal circuit is cut off from the outside, it has the effect of completely preventing erroneous writing that occurs after data is written.

[Brief explanation of the drawing]

Fig. 1 is a time chart for explaining the write operation of a PROM which has dedicated terminals, Fig. 2a is a plan view showing the main part of the first embodiment of the present invention, and Fig. 2b is the same as that shown in Fig. 1. Figure 3 is a partially enlarged plan view of the package cage in a with the lid removed.
FIG. 2 is a circuit diagram showing a main part of the embodiment. 1...PROM, 2, 12...Program () terminal, 3...Chip, 4, 13...Wiring, 5...Thin wire, 6...Window for cutting thin wire, 7...Window for erasing memory, 11... ...Internal circuit, 14...Fuse, 15...No connection (NC) terminal.

Claims (1)

[Scope of utility model registration request] In a programmable read-only memory having a dedicated program terminal that is connected to an internal circuit and controls writing to the internal circuit, a thin wire is connected between the wiring as a signal path from the program terminal to the internal circuit and the program terminal. Connect the wires,
A programmable read-only memory characterized by having a thin wire cutting window provided at this connection point.