HANBit
FUNCTIONAL DESCRIPTION
HMN4M8D
The HMN4M8D executes a read cycle whenever /WE is inactive(high) and /CE is active(low). The address specified by the
address inputs(A
0
-A19) defines which of the 4,194,304 bytes of data is accessed. Valid data will be available to the eight
data output drivers within t
ACC
(access time) after the last address input signal is stable.
When power is valid, the HMN4M8D operates as a standard CMOS SRAM. During power-down and power-up cycles, the
HMN4M8D acts as a nonvolatile memory, automatically protecting and preserving the memory contents.
The HMN4M8D is in the write mode whenever the /WE and /CE signals are in the active (low) state after address inputs
are stable. The later 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 /CE or /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
WR
) before another cycle can be initiated. The /OE control
signal should be kept inactive (high) during write cycles to avoid bus contention. However, if the output bus been enabled
(/CE and /OE active) then /WE will disable the outputs in t
ODW
from its falling edge.
The HMN4M8D provides full functional capability for Vcc greater than 4.5 V and write protects by 4.37 V nominal. Power-
down/power-up control circuitry constantly monitors the Vcc supply for a power-fail-detect threshold V
PFD
. When V
CC
falls
below the V
PFD
threshold, the SRAM automatically write-protects the data. All inputs to the RAM become
“don’t
care” and
all outputs are high impedance. As Vcc falls below approximately 3 V, the power switching circuit connects the lithium
energy soure to RAM to retain data. During power-up, when Vcc rises above approximately 3.0 volts, the power switching
circuit connects external Vcc to the RAM and disconnects the lithium energy source. Normal RAM operation can resume
after Vcc exceeds 4.5 volts.
BLOCK DIAGRAM
`
/OE
/WE
4 x 1024K x 8
SRAM
Block
PIN DESCRIPTION
A
0
-A
19
DQ
0
-DQ
7
A
0
-A
21
: Address Input
/CE : Chip Enable
V
SS
: Ground
Power
/CE
A
20
A
21
/CE
CON
V
CC
DQ
0
-DQ
7
: Data In / Data Out
/WE : Write Enable
Power
–
Fail
Control
/OE : Output Enable
V
CC
: Power (+5V)
Lithium
Cell
NC : No Connection
URL : www.hbe.co.kr
Rev. 1.0 (May, 2002)
2
HANBit Electronics Co.,Ltd
HANBIT [ HANBIT ELECTRONICS CO.,LTD ]
