X84256 Datasheet, PDF (4/15 Pages) Xicor Inc. – UPort Saver EEPROM

X84256
Preliminary
CE
OE
WE
I/O (IN)
I/O (OUT)
"0"
A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
"1"
"0"
RESET
WHEN ACCESSING: X84256 ARRAY: A15=0
LOAD ADDRESS
LOAD DATA
START
NONVOLATILE
WRITE
Figure 2. Write Sequence
The nonvolatile write cycle is initiated by issuing a special
read/write “1”/read sequence. The first read cycle ends
the page load, then the write “1” followed by a read starts
the nonvolatile write cycle. The device recognizes 64-
byte pages (e.g., beginning at addresses XXXXXXXXX
000000 for X84256).
When sending data to the part, attempts to exceed the
upper address of the page will result in the address
counter “wrapping-around” to the first address on the
page, where data loading can continue. For this reason,
sending more than 512 consecutive data bits will result in
overwriting previous data.
result: I/O is LOW as long as a nonvolatile write cycle is
in progress, and l/O is HIGH when the nonvolatile write
cycle is done.
Low Power Operation
The device enters an idle state, which draws minimal
current when:
• an illegal sequence is entered. The following are the
more common illegal sequences:
—Read/Write/Write—any time
—Read/Write ‘1’—When writing the address or writ-
ing data.
A nonvolatile write cycle will not start if a partial or incom-
plete write sequence is issued. The internal write enable
latch is reset when the nonvolatile write cycle is com-
pleted and after an invalid write to prevent inadvertent
writes. Note that this sequence is fully static, with no spe-
cial timing restrictions. The processor is free to perform
other tasks on the bus whenever the chip enable pin
(CE) is HIGH.
Nonvolatile Write Status
The status of a nonvolatile write cycle can be determined
at any time by simply reading the state of the l/O pin on
the device. This pin is read when OE and CE are LOW
and WE is HIGH. During a nonvolatile write cycle the l/O
pin is LOW. When the nonvolatile write cycle is complete,
the l/O pin goes HIGH. A reset sequence can also be
issued during a nonvolatile write cycle with the same
SYMBOL TABLE
WAVEFORM INPUTS
OUTPUTS
Must be
steady
Will be
steady
May change
from LOW to
HIGH
May change
from HIGH to
LOW
Don’t Care:
Changes
Allowed
N/A
Will change
from LOW to
HIGH
Will change
from HIGH to
LOW
Changing:
State Not
Known
Center Line
is High
Impedance
4