28F002BC Ver la hoja de datos (PDF) - Intel
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28F002BC Datasheet PDF : 37 Pages
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28F002BC 2-MBIT BOOT BLOCK FLASH MEMORY
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
Register command to the CUI. After writing this
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
register is updated; otherwise, the completion of a
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
register bits).
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 Register command is
PRELIMINARY
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
register, or intelligent identifier.
3.3.3
PROGRAM MODE
Programming is executed using a 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:
1. Program the desired bits of the addressed
memory byte.
2. 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
register is a “0.” The status register can be polled
by toggling either CE# or OE# to determine when
the program sequence is complete. Only the Read
Status Register command is 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
register is set to a “1” to indicate a program failure.
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 follow after programming is completed;
however, reads from the memory array cannot be
accomplished until the CUI is given the Read Array
command. Figure 7 shows the Automated
Programming Flowchart.
17
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