Datasheet

Writing with Verication
To write data to the DS2431, the scratchpad must be
used as intermediate storage. First, the master issues
the Write Scratchpad command to specify the desired
target address, followed by the data to be written to the
scratchpad. Note that Copy Scratchpad commands must
be performed on 8-byte boundaries, i.e., the three LSBs
of the target address (T2, T1, T0) must be equal to 000b.
If T[2:0] are sent with nonzero values, the copy func-
tion is blocked. Under certain conditions (see the Write
Scratchpad [0Fh] section) the master receives an inverted
CRC-16 of the command, address (actual address sent),
and data at the end of the Write Scratchpad command
sequence. Knowing this CRC value, the master can
compare it to the value it has calculatedto decide if the
communication was successful and proceed to the Copy
Scratchpad command. If the master could not receive the
CRC-16, it should send the Read Scratchpad command to
verify data integrity. As a preamble to the scratchpad data,
the DS2431 repeats the target address TA1 and TA2 and
sends the contents of the E/S register. If the PF flag is set,
data did not arrive correctly in the scratchpad, or there was
a loss of power since data was last written to the scratch-
pad. The master does not need to continue reading; it can
start a new trial to write data to the scratchpad. Similarly,
a set AA flag together with a cleared PF flag indicates that
the device did not recognize the Write command.
If everything went correctly, both flags are cleared. Now
the master can continue reading and verifying every data
byte. After the master has verified the data, it can send the
Copy Scratchpad command, for example. This command
must be followed exactly by the data of the three address
registers, TA1, TA2, and E/S. The master should obtain
the contents of these registers by reading the scratchpad.
Memory Function Commands
The Memory Function Flowchart (Figure 7) describes
the protocols necessary for accessing the memory of the
DS2431. An example on how to use these functions to
write to and read from the device is in the Memory Function
Example section. The communication between the master
and the DS2431 takes place either at standard speed
(default, OD = 0) or at overdrive speed (OD = 1). If not
explicitly set into overdrive mode, the DS2431 assumes
standard speed.
Write Scratchpad [0Fh]
The Write Scratchpad command applies to the data
memory and the writable addresses in the register page.
For the scratchpad data to be valid for copying to the
array, the user must perform a Write Scratchpad com-
mand of 8 bytes starting at a valid row boundary. The
Write Scratchpad command accepts invalid addresses
and partial rows, but subsequent Copy Scratchpad com-
mands are blocked.
After issuing the Write Scratchpad command, the master
must first provide the 2-byte target address, followed by
the data to be written to the scratchpad. The data is writ-
ten to the scratchpad starting at the byte offset of T[2:0].
The E/S bits E[2:0] are loaded with the starting byte offset
and increment with each subsequent byte. Effectively,
E[2:0] is the byte offset of the last full byte written to the
scratchpad. Only full data bytes are accepted.
When executing the Write Scratchpad command, the
CRC generator inside the DS2431 (Figure 13) calculates
a CRC of the entire data stream, starting at the command
code and ending at the last data byte as sent by the mas-
ter. This CRC is generated using the CRC-16 polynomial
by first clearing the CRC generator and then shifting in the
command code (0Fh) of the Write Scratchpad command,
the target addresses (TA1 and TA2), and all the data
bytes. Note that the CRC-16 calculation is performed with
the actual TA1 and TA2 and data sent by the master. The
master can end the Write Scratchpad command at any
time. However, if the end of the scratchpad is reached
(E[2:0] = 111b), the master can send 16 read time slots
and receive the CRC generated by the DS2431.
If a Write Scratchpad command is attempted to a write-
protected location, the scratchpad is loaded with the data
already existing in memory rather than the data transmitted.
Similarly, if the target address page is in EPROM mode,
the scratchpad is loaded with the bitwise logical AND of the
transmitted data and data already existing in memory.
DS2431 1024-Bit, 1-Wire EEPROM
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