M25PE40 データシートの表示（PDF） - STMicroelectronics
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M25PE40 Datasheet PDF : 37 Pages
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M25PE40
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 driv-
en High, the Write cycle starts. The remaining,
unchanged, Bytes of the data buffer are automati-
cally loaded with the values of the corresponding
Bytes of the addressed memory page. The ad-
dressed memory page then automatically put into
an Erase cycle. Finally, the addressed memory
page is programmed 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.
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 al-
ready 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 chang-
es involve resetting bits to 0 that are still set to
1. When this method is possible, it has the ad-
ditional advantage of minimizing the number
of unnecessary erase operations, and the ex-
tra stress incurred by each page.
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
mode until the Release from Deep Power-down in-
struction is executed.
All other instructions are ignored while the device
is in the Deep Power-down mode. This can be
used as an extra software protection mechanism,
when the device is not in active use, to protect the
device from inadvertent Write, Program or Erase
instructions.
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