M48Z128, M48Z128Y Operating modes
Doc ID 2426 Rev 6 7/20
2 Operating modes
The M48Z128/Y also has its own power-fail detect circuit. The control circuitry constantly
monitors the single V
CC
supply for an out of tolerance condition. When V
CC
is out of
tolerance, the circuit write protects the SRAM, providing a high degree of data security in the
midst of unpredictable system operation brought on by low V
CC
. As V
CC
falls below the
switchover voltage (V
SO
), the control circuitry connects the battery which maintains data
until valid power returns.
Table 2. Operating modes
Note: X = V
IH
or V
IL
; V
SO
= battery backup switchover voltage.
2.1 READ mode
The M48Z128/Y is in the READ mode whenever W (WRITE enable) is high and E (chip
enable) is low. The device architecture allows ripple-through access of data from eight of
1,048,576 locations in the static storage array. Thus, the unique address specified by the 17
address inputs defines which one of the 131,072 bytes of data is to be accessed. Valid data
will be available at the data I/O pins within address access time (t
AVQV
) after the last
address input signal is stable, providing that the E
and G (output enable) access times are
also satisfied. If the E
and G access times are not met, valid data will be available after the
later of chip enable access time (t
ELQV
) or output enable access time (t
GLQV
). The state of
the eight three-state data I/O signals is controlled by E
and G. If the outputs are activated
before t
AVQV
, the data lines will be driven to an indeterminate state until t
AVQV
. If the address
inputs are changed while E
and G remain low, output data will remain valid for output data
hold time (t
AXQX
) but will go indeterminate until the next address access.
Mode V
CC
E G W DQ0-DQ7 Power
Deselect
4.75 to 5.5 V
or
4.5 to 5.5 V
V
IH
X X High Z Standby
WRITE V
IL
XV
IL
D
IN
Active
READ V
IL
V
IL
V
IH
D
OUT
Active
READ V
IL
V
IH
V
IH
High Z Active
Deselect V
SO
to V
PFD
(min)
(1)
1. See Table 10 on page 15 for details.
X X X High Z CMOS standby
Deselect ≤ V
SO
(1)
X X X High Z Battery backup mode
Obsolete Product(s) - Obsolete Product(s)
