2 Mbit Flash + 1 Mbit SRAM ComboMemory
SST31LF021 / SST31LF021E
Data Sheet
after the rising edge of the sixth WE# (or BEF#) pulse. See
Figure 7 for Data# Polling timing diagram and Figure 17 for
a flowchart.
Concurrent Read and Write Operations
The SST31LF021/021E provide the unique benefit of
being able to read from or write to SRAM, while simulta-
neously erasing or programming the flash. The device will
ignore all SDP commands when an Erase or Program
operation is in progress. This allows data alteration code to
be executed from SRAM, while altering the data in flash.
The following table lists all valid states. SST does not rec-
ommend that both bank enables, BEF# and BES#, be
simultaneously asserted.
Flash Toggle Bit (DQ6)
During the internal Program or Erase operation, any con-
secutive attempts to read DQ6 will produce alternating 0s
and 1s, i.e., toggling between 0 and 1. When the internal
Program or Erase operation is completed, the toggling will
stop. The flash memory bank is then ready for the next
operation. The Toggle Bit is valid after the rising edge of the
fourth WE# (or BE#) pulse for Program operation. For Sec-
tor or Bank-Erase, the Toggle Bit is valid after the rising
edge of the sixth WE# (or BEF#) pulse. See Figure 8 for
Toggle Bit timing diagram and Figure 17 for a flowchart.
CONCURRENT READ/WRITE STATE TABLE
Flash
SRAM
Read
Write
Program/Erase
Program/Erase
Flash Memory Data Protection
Note that Product Identification commands use SDP;
therefore, these commands will also be ignored while an
Erase or Program operation is in progress.
The SST31LF021/021E flash memory bank provides both
hardware and software features to protect nonvolatile data
from inadvertent writes.
Product Identification
Flash Hardware Data Protection
The Product Identification mode identifies the devices as
either SST31LF021 or SST31LF021E and the manufac-
turer as SST. This mode may be accessed by hardware or
software operations. The hardware device ID Read opera-
tion is typically used by a programmer to identify the correct
algorithm for the SST31LF021/021E flash memory banks.
Users may wish to use the software Product Identification
operation to identify the part (i.e., using the device ID) when
using multiple manufacturers in the same socket. For
details, see Table 3 for hardware operation or Table 4 for
software operation, Figure 11 for the software ID entry and
read timing diagram and Figure 18 for the ID entry com-
mand sequence flowchart.
Noise/Glitch Protection: A WE# or BEF# pulse of less than
5 ns will not initiate a Write cycle.
VDD Power Up/Down Detection: The Write operation is
inhibited when is less than 1.5V.
Write Inhibit Mode: Forcing OE# low, BEF# high, or WE#
high will inhibit the Flash Write operation. This prevents
inadvertent writes during power-up or power-down.
Flash Software Data Protection (SDP)
The SST31LF021/021E provide the JEDEC approved
Software Data Protection scheme for all flash memory
bank data alteration operations, i.e., Program and Erase.
Any Program operation requires the inclusion of a series of
three-byte sequence. The three-byte load sequence is
used to initiate the Program operation, providing optimal
protection from inadvertent Write operations, e.g., during
the system power-up or power-down. Any Erase operation
requires the inclusion of six-byte load sequence. The
SST31LF021/021E devices are shipped with the Software
Data Protection permanently enabled. See Table 4 for the
specific software command codes. During SDP command
sequence, invalid SDP commands will abort the device to
the Read mode, within TRC.
TABLE 1: PRODUCT IDENTIFICATION
Address
Data
Manufacturer’s ID
Device ID
0000H
BFH
SST31LF021
SST31LF021E
0001H
0001H
18H
19H
T1.4 392
Product Identification Mode Exit/Reset
In order to return to the standard Read mode, the Software
Product Identification mode must be exited. Exiting is
accomplished by issuing the Exit ID command sequence,
which returns the device to the Read operation. Please
note that the software reset command is ignored during an
©2001 Silicon Storage Technology, Inc.
S71137-03-000 10/01 392
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SST [ SILICON STORAGE TECHNOLOGY, INC ]
