M28W640CT Datasheet, PDF(19/54 Page) STMicroelectronics – 64 Mbit 4Mb x16, Boot Block 3V Supply Flash Memory

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M28W640CT Datasheet, PDF (19/54 Pages) STMicroelectronics – 64 Mbit 4Mb x16, Boot Block 3V Supply Flash Memory

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M28W640CT, M28W640CB

STATUS REGISTER

The Status Register provides information on the

current or previous Program or Erase operation.

The various bits convey information and errors on

the operation. To read the Status register the

Read Status Register command can be issued, re-

fer to Read Status Register Command section. To

output the contents, the Status Register is latched

on the falling edge of the Chip Enable or Output

Enable signals, and can be read until Chip Enable

or Output Enable returns to VIH. Either Chip En-

able or Output Enable must be toggled to update

the latched data.

Bus Read operations from any address always

read the Status Register during Program and

Erase operations.

The bits in the Status Register are summarized in

Table 10, Status Register Bits. Refer to Table 10

in conjunction with the following text descriptions.

Program/Erase Controller Status (Bit 7). The Pro-

gram/Erase Controller Status bit indicates whether

the Program/Erase Controller is active or inactive.

When the Program/Erase Controller Status bit is

Low (set to â0â), the Program/Erase Controller is

active; when the bit is High (set to â1â), the Pro-

gram/Erase Controller is inactive, and the device

is ready to process a new command.

The Program/Erase Controller Status is Low im-

mediately after a Program/Erase Suspend com-

mand is issued until the Program/Erase Controller

pauses. After the Program/Erase Controller paus-

es the bit is High .

During Program, Erase, operations the Program/

Erase Controller Status bit can be polled to find the

end of the operation. Other bits in the Status Reg-

ister should not be tested until the Program/Erase

Controller completes the operation and the bit is

High.

After the Program/Erase Controller completes its

operation the Erase Status, Program Status, VPP

Status and Block Lock Status bits should be tested

for errors.

Erase Suspend Status (Bit 6). The Erase Sus-

pend Status bit indicates that an Erase operation

has been suspended or is going to be suspended.

When the Erase Suspend Status bit is High (set to

â1â), a Program/Erase Suspend command has

been issued and the memory is waiting for a Pro-

gram/Erase Resume command.

The Erase Suspend Status should only be consid-

ered valid when the Program/Erase Controller Sta-

tus bit is High (Program/Erase Controller inactive).

Bit 7 is set within 30Âµs of the Program/Erase Sus-

pend command being issued therefore the memo-

ry may still complete the operation rather than

entering the Suspend mode.

When a Program/Erase Resume command is is-

sued the Erase Suspend Status bit returns Low.

Erase Status (Bit 5). The Erase Status bit can be

used to identify if the memory has failed to verify

that the block has erased correctly. When the

Erase Status bit is High (set to â1â), the Program/

Erase Controller has applied the maximum num-

ber of pulses to the block and still failed to verify

that the block has erased correctly. The Erase Sta-

tus bit should be read once the Program/Erase

Controller Status bit is High (Program/Erase Con-

troller inactive).

Once set High, the Erase Status bit can only be re-

set Low by a Clear Status Register command or a

hardware reset. If set High it should be reset be-

fore a new Program or Erase command is issued,

otherwise the new command will appear to fail.

Program Status (Bit 4). The Program Status bit

is used to identify a Program failure. When the

Program Status bit is High (set to â1â), the Pro-

gram/Erase Controller has applied the maximum

number of pulses to the byte and still failed to ver-

ify that it has programmed correctly. The Program

Status bit should be read once the Program/Erase

Controller Status bit is High (Program/Erase Con-

troller inactive).

Once set High, the Program Status bit can only be

reset Low by a Clear Status Register command or

a hardware reset. If set High it should be reset be-

fore a new command is issued, otherwise the new

command will appear to fail.

VPP Status (Bit 3). The VPP Status bit can be

used to identify an invalid voltage on the VPP pin

during Program and Erase operations. The VPP

pin is only sampled at the beginning of a Program

or Erase operation. Indeterminate results can oc-

cur if VPP becomes invalid during an operation.

When the VPP Status bit is Low (set to â0â), the volt-

age on the VPP pin was sampled at a valid voltage;

when the VPP Status bit is High (set to â1â), the VPP

pin has a voltage that is below the VPP Lockout

Voltage, VPPLK, the memory is protected and Pro-

gram and Erase operations cannot be performed.

Once set High, the VPP Status bit can only be reset

Low by a Clear Status Register command or a

hardware reset. If set High it should be reset be-

fore a new Program or Erase command is issued,

otherwise the new command will appear to fail.

Program Suspend Status (Bit 2). The Program

Suspend Status bit indicates that a Program oper-

ation has been suspended. When the Program

Suspend Status bit is High (set to â1â), a Program/

Erase Suspend command has been issued and

the memory is waiting for a Program/Erase Re-

sume command. The Program Suspend Status

should only be considered valid when the Pro-

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