W29C040P-90 Winbond Electronics, W29C040P-90 Datasheet - Page 4

• Manufacturer Part Number: W29C040P-90
• Manufacturer: Winbond Electronics

Specifications of W29C040P-90

• Density: 4Mb
• Access Time (max): 90ns
• Interface Type: Parallel
• Boot Type: Bottom/Top
• Address Bus: 19b
• Operating Supply Voltage (typ): 5V
• Operating Temp Range: 0C to 70C
• Package Type: PLCC
• Program/erase Volt (typ): 5V
• Sync/async: Asynchronous
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (min): 4.5V
• Operating Supply Voltage (max): 5.5V
• Word Size: 8b
• Number Of Words: 512K
• Supply Current: 50mA
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / Rohs Status: Not Compliant

6. FUNCTIONAL DESCRIPTION
6.1
The read operation of the W29C040 is controlled by #CE and #OE, both Chip 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 read cycle timing waveforms for further details.
6.2
The W29C040 is written (erased/programmed) on a page basis. Every page contains 256 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 "FF hex" during the write operation 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 write (erase/program) 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
200 μS after the initial byte-load cycle, the W29C040 will stay in the page load cycle. Additional bytes
can then be loaded consecutively. The page load cycle will be terminated and the internal write
(erase/program) cycle will start if no additional byte is loaded into the page buffer. A8 to A18 specify
the page address. All bytes that are loaded into the page buffer must have the same page address.
A0 to A7 specify the byte address within the page. The bytes may be loaded in any order; sequential
loading is not required.
In the internal write cycle, all data in the page buffers, i.e., 256 bytes of data, are written
simultaneously into the memory array. The typical write (erase/program) time is 5 mS. The entire
memory array can be written in 10.4 seconds. Before the completion of the internal write 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.
6.3
The device provides a JEDEC-approved optional software-protected data write. Once this scheme is
enabled, any write operation requires a three-byte command sequence (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 W29C040 is shipped with the software data protection 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 command sequence cycle. Once enabled, the software data protection will
remain enabled unless the disable commands are issued. A power transition will not reset the
Read Mode
Page Write Mode
Software-protected Data Write
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W29C040
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