DS1248 Maxim, DS1248 Datasheet - Page 4

• Manufacturer Part Number: DS1248
• Description: The DS1248 1024K NV SRAM with Phantom Clock is a fully static nonvolatile RAM (organized as 128K words by 8 bits) with a built-in real-time clock
• Manufacturer: Maxim

RAM READ MODE
The DS1248 executes a read cycle whenever WE (write enable) is inactive (high) and CE (chip enable) is
active (low). The unique address specified by the 17 address inputs (A0–A16) defines which of the 128k
bytes of data is to be accessed. Valid data will be available to the eight data-output drivers within t
(access time) after the last address input signal is stable, providing that CE and OE (output enable) access
times and states are also satisfied. If OE and CE access times are not satisfied, then data access must be
measured from the later occurring signal (CE or OE) and the limiting parameter is either t
for OE, rather than address access.
RAM WRITE MODE
The DS1248 is in the write mode whenever the WE and CE signals are in the active (low) state after
address inputs are stable. The latter occurring falling edge of CE or WE will determine the start of the
write cycle. The write cycle is terminated by the earlier rising edge of CEor WE. All address inputs must
be kept valid throughout the write cycle. WE must return to the high state for a minimum recovery time
(t
write cycles to avoid bus contention. However, if the output bus has been enabled (CE and OE active)
then WE will disable the outputs in t
DATA RETENTION MODE
The 5V device is fully accessible and data can be written or read only when V
However, when V
internal clock registers and SRAM are blocked from any access. When V
point, V
operation and SRAM data are maintained from the battery until V
The 3.3V device is fully accessible and data can be written or read only when V
When V
switched from V
the device power is switched from V
operation and SRAM data are maintained from the battery until V
All control, data, and address signals must be powered down when V
WR
) before another cycle can be initiated. The OE control signal should be kept inactive (high) during
SO
CC
(battery supply level), device power is switched from the V
falls below V
CC
CC
to the backup supply (V
is below the power-fail point, V
PF
, access to the device is inhibited. If V
ODW
CC
to the backup supply (V
from its falling edge.
BAT
) when V
4 of 19
PF
CC
(point at which write protection occurs), the
drops below V
BAT
PF
CC
CC
is less than V
is returned to nominal levels.
is returned to nominal levels.
) when V
CC
CC
is powered-down.
CC
pin to the backup battery. RTC
PF
falls below the battery switch
. If V
CC
drops below V
BAT
PF
CC
CC
, the device power is
is greater than V
is greater than V
is greater than V
CO
for CE or t
BAT
. RTC
BAT
ACC
PF
OE
PF
.
,
.