U632H64
Device Operation
Figure 1 shows the proper connection of capacitors for
automatic STORE operation. The charge storage capa-
citor should have a capacity of 100 μF ( 20 %) at 6 V.
Each U632H64 must have its own 100 μF capacitor.
Each U632H64 must have a high quality, high fre-
quency bypass capacitor of 0.1 μF connected between
The U632H64 has two separate modes of operation:
SRAM mode and nonvolatile mode. In SRAM mode,
the memory operates as a standard fast static RAM. In
nonvolatile mode, data is transferred from SRAM to
EEPROM (the STORE operation) or from EEPROM to
SRAM (the RECALL operation). In this mode SRAM
functions are disabled.
STORE cycles may be initiated under user control via a
software sequence or HSB assertion and are also auto-
matically initiated when the power supply voltage level
of the chip falls below VSWITCH. RECALL operations are
automatically initiated upon power up and may occur
also when VCCX rises above VSWITCH after a low power
condition. RECALL cycles may also be initiated by a
software sequence.
VCAP and VSS, using leads and traces that are as short
as possible. This capactior do not replace the normal
expected high frequency bypass capacitor between the
power supply voltage and VSS.
In order to prevent unneeded STORE operations, auto-
matic STOREs as well as those initiated by externally
driving HSB LOW will be ignored unless at least one
WRITE operation has taken place since the most
recent STORE cycle. Note that if HSB is driven LOW
via external circuitry and no WRITEs have taken place,
the part will still be disabled until HSB is allowed to
return HIGH. Software initiated STORE cycles are per-
formed regardless of whether or not a WRITE opera-
tion has taken place.
SRAM READ
The U632H64 performs a READ cycle whenever E and
G are LOW and HSB and W are HIGH. The address
specified on pins A0 - A12 determines which of the
8192 data bytes will be accessed. When the READ is
initiated by an address transition, the outputs will be
valid after a delay of tcR. If the READ is initiated by E or
G, the outputs will be valid at ta(E) or at ta(G), whichever
is later. The data outputs will repeatedly respond to
address changes within the tcR access time without the
need for transition on any control input pins, and will
remain valid until another address change or until E or
G is brought HIGH or W or HSB is brought LOW.
Automatic RECALL
During power up an automatic RECALL takes place. At
a low power condition (power supply voltage < VSWITCH
)
an internal RECALL request may be latched. As soon
as power supply voltage exceeds again the sense
voltage of VSWITCH, a requested RECALL cycle will
automatically be initiated and will take tRESTORE to com-
plete.
If the U632H64 is in a WRITE state at the end of a
power up RECALL, the SRAM data will be corrupted.
To help avoid this situation, a 10 KΩ resistor should be
connected between W and power supply voltage.
SRAM WRITE
A WRITE cycle is performed whenever E and W are
LOW and HSB is HIGH. The address inputs must be
stable prior to entering the WRITE cycle and must
remain stable until either E or W goes HIGH at the end
of the cycle. The data on pins DQ0 - 7 will be written
into the memory if it is valid tsu(D) before the end of a W
controlled WRITE or tsu(D) before the end of an E con-
trolled WRITE.
It is recommended that G is kept HIGH during the
entire WRITE cycle to avoid data bus contention on the
common I/O lines. If G is left LOW, internal circuitry will
turn off the output buffers tdis(W) after W goes LOW.
Software Nonvolatile STORE
The U632H64 software controlled STORE cycle is
initiated by executing sequential READ cycles from six
specific address locations. By relying on READ cycles
only, the U632H64 implements nonvolatile operation
while remaining compatible with standard 8K x 8
SRAMs. During the STORE cycle, an erase of the pre-
vious nonvolatile data is performed first, followed by
parallel programming of all nonvolatile elements. Once
a STORE cycle is initiated, further inputs and outputs
are disabled until the cycle is completed.
Because a sequence of addresses is used for STORE
initiation, it is important that no other READ or WRITE
accesses intervene in the sequence or the sequence
will be aborted.
To initiate the STORE cycle the following READ
sequence must be performed:
Automatic STORE
During normal operation, the U632H64 will draw cur-
rent from VCCX to charge up a capacitor connected to
the VCAP pin. This stored charge will be used by the
chip to perform a single STORE operation. If the
voltage on the VCCX pin drops below VSWITCH, the part
will automatically disconnect the VCAP pin from VCCX
and initiate a STORE operation.
August 15, 2006
STK Control #ML0047
11
Rev 1.1
SIMTEK [ SIMTEK CORPORATION ]
