Protection after brown out in a synchronous memory

Details Protection after brown out in a synchronous memory Protection after brown out in a synchronous memory

2001-05-22

2002-04-02

Nguyen, Tan T. (Department: 2818)

Static information storage and retrieval

Powering

C365S228000

Reexamination Certificate

active

06366521

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to non-volatile memory devices and in particular the present invention relates to a synchronous non-volatile flash memory.
BACKGROUND OF THE INVENTION
Memory devices are typically provided as internal storage areas in the computer. The term memory identifies data storage that comes in the form of integrated circuit chips. There are several different types of memory. One type is RAM (random-access memory). This is typically used as main memory in a computer environment. RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon-as the power is turned off, whatever data was in RAM is lost.
Computers almost always contain a small amount of read-only memory (ROM) that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. An EEPROM (electrically erasable programmable read-only memory) is a special type non-volatile ROM that can be erased by exposing it to an electrical charge. Like other types of ROM, EEPROM is traditionally not as fast as RAM. EEPROM comprise a large number of memory cells having electrically isolated gates (floating gates). Data is stored in the memory cells in the form of charge on the floating gates. Charge is transported to or removed from the floating gates by programming and erase operations, respectively.
Yet another type of non-volatile memory is a Flash memory. A Flash memory is a type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCS have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.
A typical Flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. Each of the memory cells includes a floating gate field-effect transistor capable of holding a charge. The cells are usually grouped into blocks. Each of the cells within a block can be electrically programmed in a random basis by charging the floating gate. The charge can be removed from the floating gate by a block erase operation. The data in a cell is determined by the presence or absence of the charge in the floating gate.
A synchronous DRAM (SDRAM) is a type of DRAM that can run at much higher clock speeds than conventional DRAM memory. SDRAM synchronizes itself with a CPU's bus and is capable of running at 100 MHZ, about three times faster than conventional FPM (Fast Page Mode) RAM, and about twice as fast EDO (Extended Data Output) DRAM and BEDO (Burst Extended Data Output) DRAM. SDRAM's can be accessed quickly, but are volatile. Many computer systems are designed to operate using SDRAM, but would benefit from non-volatile memory.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a non-volatile memory device that can operate in a manner similar to SDRAM operation.
SUMMARY OF THE INVENTION
The above-mentioned problems with memory devices and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a memory device comprises a voltage detection circuit to monitor a supply voltage and provide a signal if the supply voltage drops below a predetermined value, and a latch coupled to the voltage detection circuit. The latch can be programmed to indicate if the supply voltage drops below the predetermined value.
In another embodiment, a memory device comprises a voltage detection circuit to monitor a supply voltage and provide a signal if the supply voltage drops below a predetermined value, a volatile register to store operating data, and a brown-out latch circuit programmed to a first data state after an initialization operation is performed to load the volatile register. The brown-out latch is programmed to a second state in response to the voltage detection circuit if the supply voltage drops below the predetermined value.
In yet another embodiment, a system comprises a power supply, and a memory device coupled to the power supply to receive a supply voltage. The memory device comprises a voltage detection circuit to monitor the supply voltage and provide a signal if the supply voltage drops below a predetermined value, and a latch coupled to the voltage detection circuit.
A method of operating a memory device comprising performing a first initialization operation on the memory device, changing a data state of a latch circuit from a default state to a second state after the first initialization operation, monitoring a supply voltage of the memory device, and setting the latch circuit to the default data state if the supply voltage is below a predetermined voltage.


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