W29EE012
FUNCTIONAL DESCRIPTION
Read Mode
The read operation of the W29EE012 is controlled by #CE and #OE, both of which have to be low for
the host to obtain data from the outputs. #CE is used for device selection. When #CE is high, the chip
is de-selected and only standby power will be consumed. #OE is the output control and is used to gate
data from the output pins. The data bus is in high impedance state when either #CE or #OE is high.
Refer to the timing waveforms for further details.
Page Write Mode
The W29EE012 is programmed on a page basis. Every page contains 128 bytes of data. If a byte of
data within a page is to be changed, data for the entire page must be loaded into the device. Any byte
that is not loaded will be erased to "FFh" during programming of the page.
The write operation is initiated by forcing #CE and #WE low and #OE high. The write procedure
consists of two steps. Step 1 is the byte-load cycle, in which the host writes to the page buffer of the
device. Step 2 is an internal programming cycle, during which the data in the page buffers are
simultaneously written into the memory array for non-volatile storage.
During the byte-load cycle, the addresses are latched by the falling edge of either #CE or #WE,
whichever occurs last. The data are latched by the rising edge of either #CE or #WE, whichever occurs
first. If the host loads a second byte into the page buffer within a byte-load cycle time (T
BLC
) of 200
µS,
after the initial byte-load cycle, the W29EE012 will stay in the page load cycle. Additional bytes can
then be loaded consecutively. The page load cycle will be terminated and the internal programming
cycle will start if no additional byte is loaded into the page buffer within 300
µS
(T
BLCO
) from the last
byte-load cycle, i.e., there is no subsequent #WE high-to-low transition after the last rising edge of
#WE. A
7
to A
16
specify the page address. All bytes that are loaded into the page buffer must have the
same page address. A
0
to A
6
specify the byte address within the page. The bytes may be loaded in
any order; sequential loading is not required.
In the internal programming cycle, all data in the page buffers, i.e., 128 bytes of data, are written
simultaneously into the memory array. Before the completion of the internal programming cycle, the
host is free to perform other tasks such as fetching data from other locations in the system to prepare
to write the next page.
Software-protected Data Write
The device provides a JEDEC-approved optional software-protected data write. Once this scheme is
enabled, any write operation requires a series of three-byte program commands (with specific data to a
specific address) to be performed before the data load operation. The three-byte load command
sequence begins the page load cycle, without which the write operation will not be activated. This write
scheme provides optimal protection against inadvertent write cycles, such as cycles triggered by noise
during system power-up and power-down.
The W29EE012 is shipped with the software data unprotection enabled. To enable the software data
protection scheme, perform the three-byte command cycle at the beginning of a page load cycle. The
device will then enter the software data protection mode, and any subsequent write operation must be
preceded by the three-byte program command cycle. Once enabled, the software data protection will
remain enabled unless the disable commands are issued. A power transition will not reset the software
data protection feature. To reset the device to unprotected mode, a six-byte command sequence is
required. See Table 3 for specific codes and Figure 10 for the timing diagram.
Publication Release Date: March 26, 2002
Revision A3
-3-
WINBOND [ WINBOND ]
