X28C64
64K
X28C64
5 Volt, Byte Alterable E
2
PROM
DESCRIPTION
8K x 8 Bit
FEATURES
•
•
•
•
•
•
•
•
150ns Access Time
Simple Byte and Page Write
—Single 5V Supply
—No External High Voltages or V
PP
Control
Circuits
—Self-Timed
—No Erase Before Write
—No Complex Programming Algorithms
—No Overerase Problem
Low Power CMOS
—60mA Active Current Max.
—200µA Standby Current Max.
Fast Write Cycle Times
—64 Byte Page Write Operation
—Byte or Page Write Cycle: 5ms Typical
—Complete Memory Rewrite: 0.625 sec. Typical
—Effective Byte Write Cycle Time: 78µs Typical
Software Data Protection
End of Write Detection
—DATA Polling
—Toggle Bit
High Reliability
—Endurance: 100,000 Cycles
—Data Retention: 100 Years
JEDEC Approved Byte-Wide Pinout
The X28C64 is an 8K x 8 E
2
PROM, fabricated with
Xicor’s proprietary, high performance, floating gate
CMOS technology. Like all Xicor programmable non-
volatile memories the X28C64 is a 5V only device. The
X28C64 features the JEDEC approved pinout for byte-
wide memories, compatible with industry standard RAMs.
The X28C64 supports a 64-byte page write operation,
effectively providing a 78µs/byte write cycle and en-
abling the entire memory to be typically written in 0.625
seconds. The X28C64 also features
DATA
and Toggle
Bit Polling, a system software support scheme used to
indicate the early completion of a write cycle. In addi-
tion, the X28C64 includes a user-optional software data
protection mode that further enhances Xicor’s hard-
ware write protect capability.
Xicor E
2
PROMs are designed and tested for applica-
tions requiring extended endurance. Inherent data re-
tention is greater than 100 years.
PIN CONFIGURATION
PLASTIC DIP
CERDIP
FLAT PACK
SOIC
NC
A12
A7
A6
A5
A4
A3
A2
A1
A0
I/O0
I/O1
I/O2
VSS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
X28C64
28
27
26
25
24
23
22
21
20
19
18
17
16
15
VCC
WE
NC
A8
A9
A11
OE
A10
CE
I/O7
I/O6
I/O5
I/04
I/O3
A6
A5
A4
A3
A2
A1
A0
NC
I/O0
5
6
7
8
9
10
11
12
X28C64
29
28
27
26
25
24
23
22
A8
A9
A11
NC
OE
A10
CE
I/O7
I/O6
LCC
PLCC
VCC
A12
WE
NC
NC
NC
A7
TSOP
A2
A1
A0
I/O0
I/O1
I/O2
NC
VSS
NC
I/O3
I/O4
I/O5
I/O6
I/O7
CE
A10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
A3
A4
A5
A6
A7
A12
NC
NC
VCC
NC
WE
NC
A8
A9
A11
OE
4
3
2
1 32 31 30
X28C64
13
21
14 15 16 17 18 19 20
I/O1
I/O2
VSS
NC
I/O3
I/O4
I/O5
3853 ILL F23.1
3853 FHD F03
3853 FHD F02
© Xicor, Inc. 1991, 1995 Patents Pending
3853-2.7 2/24/99 T0/C3/D2 NS
1
Characteristics subject to change without notice
X28C64
DEVICE OPERATION
Read
Read operations are initiated by both
OE
and
CE
LOW.
The read operation is terminated by either
CE
or
OE
returning HIGH. This two line control architecture elimi-
nates bus contention in a system environment. The data
bus will be in a high impedance state when either
OE
or
CE
is HIGH.
Write
Write operations are initiated when both
CE
and
WE
are
LOW and
OE
is HIGH. The X28C64 supports both a
CE
and
WE
controlled write cycle. That is, the address is
latched by the falling edge of either
CE
or
WE,
whichever
occurs last. Similarly, the data is latched internally by the
rising edge of either
CE
or
WE,
whichever occurs first.
A byte write operation, once initiated, will automatically
continue to completion, typically within 5ms.
Page Write Operation
The page write feature of the X28C64 allows the entire
memory to be written in 0.625 seconds. Page write
allows two to sixty-four bytes of data to be consecutively
written to the X28C64 prior to the commencement of the
internal programming cycle. The host can fetch data
from another device within the system during a page
write operation (change the source address), but the
page address (A
6
through A
12
) for each subsequent
valid write cycle to the part during this operation must be
the same as the initial page address.
The page write mode can be initiated during any write
operation. Following the initial byte write cycle, the host
can write an additional one to sixty-three bytes in the
same manner as the first byte was written. Each succes-
sive byte load cycle, started by the
WE
HIGH to LOW
transition, must begin within 100µs of the falling edge of
the preceding
WE.
If a subsequent
WE
HIGH to LOW
transition is not detected within 100µs, the internal
automatic programming cycle will commence. There is
no page write window limitation. Effectively the page
write window is infinitely wide, so long as the host
continues to access the device within the byte load cycle
time of 100µs.
Write Operation Status Bits
The X28C64 provides the user two write operation
status bits. These can be used to optimize a system
write cycle time. The status bits are mapped onto the
I/O bus as shown in Figure 1.
Figure 1. Status Bit Assignment
I/O
DP
TB
5
4
3
2
1
0
RESERVED
TOGGLE BIT
DATA POLLING
3853 FHD F11
DATA
Polling (I/O
7
)
The X28C64 features
DATA
Polling as a method to
indicate to the host system that the byte write or page
write cycle has completed.
DATA
Polling allows a simple
bit test operation to determine the status of the X28C64,
eliminating additional interrupt inputs or external hard-
ware. During the internal programming cycle, any at-
tempt to read the last byte written will produce the
complement of that data on I/O
7
(i.e. write data = 0xxx
xxxx, read data = 1xxx xxxx). Once the programming
cycle is complete, I/O
7
will reflect true data. Note: If the
X28C64 is in the protected state and an illegal write
operation is attempted
DATA
Polling will not operate.
Toggle Bit (I/O
6
)
The X28C64 also provides another method for deter-
mining when the internal write cycle is complete. During
the internal programming cycle I/O
6
will toggle from
HIGH to LOW and LOW to HIGH on subsequent
attempts to read the device. When the internal cycle is
complete the toggling will cease and the device will be
accessible for additional read or write operations.
3
X28C64
The Toggle Bit I/O
6
Figure 4. Toggle Bit Bus Sequence
LAST
WRITE
WE
CE
OE
I/O6
VOH
*
VOL
HIGH Z
*
X28C64
READY
* Beginning and ending state of I/O6 will vary.
3853 FHD F14
Figure 5. Toggle Bit Software Flow
The Toggle Bit can eliminate the software housekeeping
chore of saving and fetching the last address and data
written to a device in order to implement
DATA
Polling.
This can be especially helpful in an array comprised of
multiple X28C64 memories that is frequently updated.
Toggle Bit Polling can also provide a method for status
checking in multiprocessor applications. The timing
diagram in Figure 4 illustrates the sequence of events on
the bus. The software flow diagram in Figure 5 illustrates
a method for polling the Toggle Bit.
LAST WRITE
LOAD ACCUM
FROM ADDR n
COMPARE
ACCUM WITH
ADDR n
COMPARE
OK?
YES
X28C64
READY
NO
3853 FHD F15
5
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