X84161 Datasheet, PDF (4/18 Pages) Xicor Inc. – uPort Saver EEPROM

X84161/641/129
Figure 2: Write Sequence
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
LOAD ADDRESS
WHEN ACCESSING: X84161 ARRAY: A15–A11=0
X84641 ARRAY: A15–A13=0
X84129 ARRAY: A15–A14=0
LOAD DATA
START
NONVOLATILE
WRITE
7008 FRM F05.1
Write Sequence
A nonvolatile write sequence consists of sending a reset
sequence, a 16-bit address, up to 32 bytes of data, and
then a special “start nonvolatile write cycle” command
sequence.
The reset sequence is issued first (as described in the
Reset Sequence section) to set an internal write enable
latch. The address is written serially by issuing 16
separate write cycles (WE and CE LOW, OE HIGH) to
the part without any read cycles between the writes. The
address is sent serially, most significant bit first, on the
l/O pin. Up to 32 bytes of data are written by issuing a
multiple of 8 write cycles. Again, no read cycles are
allowed between writes.
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 32-
byte pages (e.g., beginning at addresses XXXXXX00000
for X84161).
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 256 consecutive data bits will result in
overwriting previous 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
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.
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