X28HC64
3
FN8109.4
June 27, 2016
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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 eliminates 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 X28HC64 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 2ms.
Page Write Operation
The page write feature of the X28HC64 allows the entire memory
to be written in 0.25 seconds. Page write allows two to sixty-four
bytes of data to be consecutively written to the X28HC64 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. Each
successive 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 X28HC64 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 2.
Pin Descriptions
SYMBOL DESCRIPTION
A
0
-A
12
Address Inputs. The Address inputs
select an 8-bit memory location
during a read or write operation.
I/O
0
-I/O
7
Data Input/Output. Data is written
to or read from the X28HC64
through the I/O pins.
WE
Write Enable. The Write Enable
input controls the writing of data to
the X28HC64.
CE
Chip Enable. The Chip Enable input
must be LOW to enable all
read/write operations. When CE is
HIGH, power consumption is
reduced.
OE
Output Enable. The Output Enable
input controls the data output
buffers and is used to initiate read
operations.
V
CC
+5V
V
SS
Ground
NC No Connect
Block Diagram
FIGURE 1. BLOCK DIAGRAM
X BUFFERS
LATCHES AND
DECODER
I/O BUFFERS
AND LATCHES
Y BUFFERS
LATCHES
DECODER
CONTROL
LOGIC AND
TIMING
65,536-BIT
EEPROM
ARRAY
I/O
0
–I/O
7
DATA INPUTS/OUTPUTS
CE
OE
V
CC
V
SS
A
0
–A
12
WE
ADDRESS
INPUTS
AND
5TBDP 43210I/O
RESERVED
TOGGLE BIT
DATA
POLLING
FIGURE 2. STATUS BIT ASSIGNMENT
