Ram/ROM hybrid memory architecture

• US 5,581,505 A
• Filed: 12/28/1994
• Issued: 12/03/1996
• Est. Priority Date: 05/15/1989
• Status: Expired due to Term

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Dallas Semiconductor Corporation (Analog Devices, Inc.)
• Inventors: Lee, Robert D.
• Primary Examiner(s): Popek, Joseph A.
• Application Number:
  US08/366,334
• Time in Patent Office: 706 Days
• Field of Search: 365/189.11, 365/225.7, 365/190, 365/154, 365/96
• US Class Current: 365/189.11
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device
• CPC Class Codes: G06F 3/04897 Special input arrangements or commands for improving display capability
• CPC Class Codes: G06K 19/047 the record carrier being shaped as a coin or a gambling token
• CPC Class Codes: G06K 19/0706 the battery being replaceable
• CPC Class Codes: G06K 19/07743 External electrical contacts
• CPC Class Codes: G06K 7/0021 for reading/sensing record carriers having surface contacts
• CPC Class Codes: G06K 7/0086 the connector comprising a circuit for steering the operations of the card connector
• CPC Class Codes: G11C 5/00 Details of stores covered by group G11C11/00
• CPC Class Codes: G11C 5/066 Means for reducing external access-lines for a semiconductor memory clip, e.g. by multiplexing at least address and data signals
• CPC Class Codes: G11C 7/24 Memory cell safety or protection circuits, e.g. arrangements for preventing inadvertent reading or writing; Status cells; Test cells
• CPC Class Codes: G11C 8/20 Address safety or protection circuits, i.e. arrangements for preventing unauthorized or accidental access

Abstract

An integrated circuit memory which includes at least some RAM/ROM hybrid columns. The RAM/ROM hybrid cells operate as normal SRAM cells forever, unless and until they are programmed to operate as ROM cells. Thus users who need the extra security permitted by ROM encoding can have this capability, while users who do not need ROM encoding can use off-the-shelf parts as RAM only.

Claims

1. A memory cell, comprising:

(a) a latch having a first node and a second node;

(b) a first pass transistor and a second pass transistor, said first pass transistor and said second pass transistor controlled by a first control line, said first pass transistor and said second pass transistor operable to electrically couple said first node and said second node of said latch to a respective bit line pair;

(c) at least one shorting element, with a first shorting element electrically coupled to said first node of said latch to pull said first node toward a constant potential; and

(d) said at least one shorting element including a fuse and a switching transistor, said switching transistor connected in series with said fuse.

2. A memory cell as recited in claim 1, wherein:

(a) said fuse is a programmable fuse.

3. A memory cell as recited in claim 1, wherein:

(a) said fuse is a laser programmable fuse.

4. A memory cell as recited in claim 1, and further comprising:

(a) a second control line connected to said switching transistor, said second control line for controlling said switching transistor.

5. A memory cell, comprising:

(a) a latch having a first node and a second node;

(b) a first pass transistor and a second pass transistor, said first pass transistor and said second pass transistor controlled by a first control line, said first pass transistor and said second pass transistor operable to electrically couple said first node and said second node of said latch to a respective bit line pair;

(c) a plurality of nonvolatile shorting elements, with a first shorting element electrically coupled to said first node of said latch to pull said first node toward a constant potential, and a second shorting element electrically coupled to said second node of said latch to pull said second node toward a constant potential;

(e) each of said plurality of nonvolatile shorting elements including a fuse; and

(f) a switching transistor connected in series with said fuse;

(g) wherein each of said switching transistors are commonly controlled by a second control line.

6. A memory cell as recited in claim 5, wherein:

(a) at least one of said fuses is a programmable fuse.

7. A memory cell as recited in claim 5, wherein:

(a) at least one of said fuses is a laser programmable fuse.