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M45PE40 Datasheet(PDF) 7 Page - STMicroelectronics

Part No. M45PE40
Description  4 Mbit, Low Voltage, Page-Erasable Serial Flash Memory With Byte-Alterability and a 33 MHz SPI Bus Interface
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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M45PE40 Datasheet(HTML) 7 Page - STMicroelectronics

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M45PE40
OPERATING FEATURES
Sharing the Overhead of Modifying Data
To write or program one (or more) data bytes, two
instructions are required: Write Enable (WREN),
which is one byte, and a Page Write (PW) or Page
Program (PP) sequence, which consists of four
bytes plus data. This is followed by the internal cy-
cle (of duration tPW or tPP).
To share this overhead, the Page Write (PW) or
Page Program (PP) instruction allows up to 256
bytes to be programmed (changing bits from 1 to
0) or written (changing bits to 0 or 1) at a time, pro-
vided that they lie in consecutive addresses on the
same page of memory.
An Easy Way to Modify Data
The Page Write (PW) instruction provides a con-
venient way of modifying data (up to 256 contigu-
ous bytes at a time), and simply requires the start
address, and the new data in the instruction se-
quence.
The Page Write (PW) instruction is entered by
driving Chip Select (S) Low, and then transmitting
the instruction byte, three address bytes (A23-A0)
and at least one data byte, and then driving Chip
Select (S) High. While Chip Select (S) is being
held Low, the data bytes are written to the data
buffer, starting at the address given in the third ad-
dress byte (A7-A0). When Chip Select (S) is driven
High, the Write cycle starts. The remaining, un-
changed, bytes of the data buffer are automatically
loaded with the values of the corresponding bytes
of the addressed memory page. The addressed
memory page then automatically put into an Erase
cycle. Finally, the addressed memory page is pro-
grammed with the contents of the data buffer.
All of this buffer management is handled internally,
and is transparent to the user. The user is given
the facility of being able to alter the contents of the
memory on a byte-by-byte basis.
For optimized timings, it is recommended to use
the Page Write (PW) instruction to write all con-
secutive targeted Bytes in a single sequence ver-
sus using several Page Write (PW) sequences
with each containing only a few Bytes (see Page
Write (PW) and AC Characteristics (33MHz oper-
ation)).
A Fast Way to Modify Data
The Page Program (PP) instruction provides a fast
way of modifying data (up to 256 contiguous bytes
at a time), provided that it only involves resetting
bits to 0 that had previously been set to 1.
This might be:
when the designer is programming the device
for the first time
when the designer knows that the page has
already been erased by an earlier Page Erase
(PE) or Sector Erase (SE) instruction. This is
useful, for example, when storing a fast
stream of data, having first performed the
erase cycle when time was available
when the designer knows that the only
changes involve resetting bits to 0 that are still
set to 1. When this method is possible, it has
the additional advantage of minimising the
number of unnecessary erase operations, and
the extra stress incurred by each page.
For optimized timings, it is recommended to use
the Page Program (PP) instruction to program all
consecutive targeted Bytes in a single sequence
versus using several Page Program (PP) se-
quences with each containing only a few Bytes
(see Page Program (PP) and AC Characteristics
(33MHz operation)).
Polling During a Write, Program or Erase Cycle
A further improvement in the write, program or
erase time can be achieved by not waiting for the
worst case delay (tPW, tPP, tPE, or tSE). The Write
In Progress (WIP) bit is provided in the Status
Register so that the application program can mon-
itor its value, polling it to establish when the previ-
ous cycle is complete.
Reset
An internal Power On Reset circuit helps protect
against inadvertent data writes. Addition protec-
tion is provided by driving Reset (Reset) Low dur-
ing the Power-on process, and only driving it High
when VCC has reached the correct voltage level,
VCC(min).
Active Power, Standby Power and Deep
Power-Down Modes
When Chip Select (S) is Low, the device is select-
ed, and in the Active Power mode.
When Chip Select (S) is High, the device is dese-
lected, but could remain in the Active Power mode
until all internal cycles have completed (Program,
Erase, Write). The device then goes in to the
Standby Power mode. The device consumption
drops to ICC1.
The Deep Power-down mode is entered when the
specific instruction (the Deep Power-down (DP) in-
struction) is executed. The device consumption
drops further to ICC2. The device remains in this


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