LH28F008SA 8M (1M × 8) Flash Memory
10
Read Array Command
Upon initial de vice powerup and after e xit from deep
powerdown mode, the LH28F008SA defaults to Read
Array mode. This operation is also initiated by writing
FFH into the Command User Interf ace. Microprocessor
read cycles retriev e arra y data. The de vice remains en-
ab led f or reads until the Command User Interf ace con-
tents are altered. Once the internal Write State Machine
has star ted a block erase or byte write operation, the
device will not recognize the Read Arra y command, until
the WSM has completed its operation. The Read Arra y
command is functional when VPP = VPPL or VPPH.
Intelligent Identifier Command
The LH28F008SA contains an intelligent identifier
operation, initiated by writing 90H into the Command
User Interface. Following the command write, a read
cycle from address 00000H retriev es the manuf acturer
code of 89H. A read cycle from address 00001H
returns the device code of A2H. To terminate the opera-
tion, it is necessary to write another valid command into
the register. Like the Read Array command, the intelli-
gent identifier command is functional when VPP = VPPL
or VPPH.
Read Status Register Command
The LH28F008SA contains a Status Register which
may be read to deter mine when a byte write or block
erase operation is complete, and whether that opera-
tion completed successfully. The Status Register may
be read at any time by writing the Read Status Register
command (70H) to the Command User Interf ace. After
writing this command, all subsequent read operations
output data from the Status Register , until another valid
command is written to the Command User Interface.
The contents of the Status Register are latched on the
falling edge of OE
»
or CE», whichever occurs last in the
read cycle. OE
»
or CE» must to toggled to VIH before
further reads to update the Status Register latch.
The Read Status Register command functions when
VPP = VPPL or VPPH.
Clear Status Register Command
The Erase Status and Byte Write Status bits are set
to '1's by the Write State Machine and can only be reset
by the Clear Status Register Command. These bits
indicate v arious f ailure conditions (see Status Register
Definitions). By allowing system software to control the
resetting of these bits, several operations may be per-
formed (such as cumulatively writing several bytes or
erasing multiple blocks in sequence). The Status Reg-
ister may then be polled to determine if an error
occurred during that sequence. This adds flexibility to
the way the device may be used.
Additionally, the VPP Status bit (SR.3) MUST be re-
set by system software before further byte writes or block
erases are attempted. To clear the Status Register , the
Clear Status Register command (50H) is written to the
Command User Interface. The Clear Status Register
command is functional when VPP = VPPL or VPPH.
Erase Setup/Erase Confirm Commands
Erase is executed one block at a time, initiated by a
two-cycle command sequence. An Erase Setup com-
mand (20H) is first written to the Command User Inter-
face, followed by the Erase Confir m command (D0H).
These commands require both appropriate sequenc-
ing and an address within the block to be erased to FFH.
Bloc k preconditioning, erase and v erify are all handled
internally by the Write State Machine, invisible to the
system. After the two-command erase sequence is writ-
ten to it, the LH28F008SA automatically outputs Status
Register data when read (see Bloc k Erase Flowchart).
The CPU can detect the completion of the erase e vent
by analyzing the output of the RY»/BY» pin, or the WSM
Status bit of the Status Register.
When erase is completed, the Erase Status bit should
be checked. If erase error is detected, the Status Reg-
ister should be cleared. The Command User Interface
remains in Read Status Register mode until further com-
mands are issued to it.
This two-step sequence of set-up followed by
execution insures that memory contents are not
accidentially erased. Also, reliable block erasure can only
occur when VPP = VPPH. In the absence of this high
voltage, memory contents are protected against era-
sure. If block erase is attempted while VPP = VPPL, the
VPP Status bit will be set to '1'. Erase attempts while
VPPL
< VPP < VPPH produce spurious results and should
not be attempted.
Erase Suspend/Erase Resume Commands
The Erase Suspend command allows block erase
interruption in order to read data from another bloc k of
memory. Once the erase process starts, writing the
Erase Suspend command (B0H) to the Command User
Interface requests that the WSM suspend the erase
sequence at a predeter mined point in the erase algo-
rithm. The LH28F008SA continues to output Status
Register data when read, after the Erase Suspend com-
mand is written to it. P olling the WSM Status and Erase
Suspend Status bits will determined when the erase
operation has been suspended (both will be set to '1').
RY»/BY» will also transition to VOH.