CAT24C44 Datasheet, PDF (7/8 Pages) Catalyst Semiconductor – 256-Bit Serial Nonvolatile CMOS Static RAM

CAT24C44
RCL/RECALL
Data is transferred from the E²PROM data memory to
RAM by either sending the RCL instruction or by pulling
the RECALL input pin low. A recall operation must be
performed before the E²PROM store, or RAM write
operations can be executed. Either a hardware or soft-
ware recall operation will set the “previous recall” latch
internal to the CAT24C44.
POWER-ON RECALL
The CAT24C44 has a power-on recall function that
transfers the E²PROM data to the RAM. After Power-up,
all functions are inhibited for at least 200ns (T_pur) from
stable V_cc.
STO/STORE
Data in the RAM memory area is stored in the E²PROM
memory either by sending the STO instruction or by
pulling the STORE input pin low. As security against any
inadvertent store operations, the following conditions
must each be met before data can be transferred into
nonvolatile storage:
• The “previous recall” latch must be set (either a
software or hardware recall operation).
• The “write enable” latch must be set (WREN
instruction issued).
• STO instruction issued or STORE input low.
During the store operation, all other CAT24C44 func-
tions are inhibited. Upon completion of the store opera-
tion, the “write enable” latch is reset. The device also
provides false store protection whenever VCC falls below
a 3.5V level. If VCC falls below this level, the store
operation is disabled and the “write enable” latch is
reset.
Figure 5. Recall Cycle Timing
RECALL
DO
tRCZ
tRCP
tRCC
HIGH-Z
tORC
Figure 6. Hardware Store Cycle Timing
STORE
DO
tSTZ
tST
tSTP
HIGH-Z
tARC
VALID DATA
UNDEFINED DATA
5157 FHD F06
5157 FHD F07
7
Doc. No. 25019-0A 2/98 N-1