28F002BC datasheet(17/37 Pages) INTEL

17 / 37 page

28F002BC 2-MBIT BOOT BLOCK FLASH MEMORY

PRELIMINARY

Erase Resume (D0H)

This command will cause the CUI to clear the

Suspend state and clear the WSM Status Bit to a

“0,” but only if an Erase Suspend command was

previously issued. Erase Resume will not have any

effect under any other conditions.

3.3.2

STATUS REGISTER

The 28F002BC contains a status register which

may be read to determine when a program or erase

operation is complete, and whether that operation

completed successfully. The status register may be

read at any time by writing the Read Status

command, all subsequent read operations output

data from the status register until another command

is written to the CUI. A Read Array command must

be written to the CUI to return to read array mode.

The status register bits are output on DQ[0:7]. The

contents of the status register are latched on

the falling edge of OE# or CE#, whichever

occurs last in the read cycle. This prevents

possible bus errors that might occur if the contents

of the status register change while reading the

status register. CE# or OE# must be toggled with

each subsequent status read to insure the status

program or erase operation will not be evident from

the status register.

When the WSM is active, the status register will

indicate the status of the WSM and upon command

completion, it will indicate success or failure of the

operation (see Table 5 for definition of status

3.3.2.1

Clearing the Status Register

The WSM sets status bits “3” through “7” to “1,” and

clears bits “6” and “7” to “0,” but cannot clear status

bits “3” through “5” to “0.” Bits 3 through 5 can only

be cleared by the controlling CPU through the use

of the Clear Status Register command. These bits

can indicate various error conditions. By allowing

the system software to control the resetting of these

bits, several operations may be performed (such as

cumulatively programming several bytes or erasing

multiple blocks in sequence). The status register

may then be read to determine if an error occurred

during that programming or erasure series. This

feature adds flexibility to the way the device may be

programmed or erased. To clear the status register,

the

Clear

Status

command

written to the CUI. Then, any other command may

be issued to the CUI. Note, again, that before a

read cycle can be initiated, a valid read command

must be written to the CUI to specify whether the

read data is to come from the memory array, status

3.3.3

PROGRAM MODE

Programming

executed

using

two-write

sequence. The Program Setup command is written

to the CUI followed by a second write which

specifies the address and data to be programmed.

The WSM then executes a sequence of internally-

timed events to:

Program the desired bits of the addressed

memory byte.

Verify that the desired bits are sufficiently

programmed.

Programming of the memory results in specific bits

within a byte being changed to a “0.”

If the user attempts to program “1”s, there will be no

change in memory contents and no error is reported

by the status register.

Similar to erasure, the status register indicates

whether programming is

complete.

While

the

program sequence is executing, bit 7 of the status

by toggling either CE# or OE# to determine when

the program sequence is complete. Only the Read

Status

command

valid

while

programming is active.

When programming is complete, the status bits,

which indicate whether the program operation was

successful, should be checked. If the programming

operation was unsuccessful, bit 4 of the status

If bit 3 is set to a “1,” then VPP was not within

acceptable limits, and the WSM did not execute the

programming sequence. If the program operation

fails, bit 4 of the status register will be set within

1.5 ms, as determined by the timeout of the WSM.

The status register should be cleared before

attempting the next operation. Any CUI instruction

can

after

programming

completed;

however, reads from the memory array cannot be

accomplished until the CUI is given the Read Array

command.

Figure

shows

the

Automated

Programming Flowchart.

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