1024-Bit, 1-Wire EEPROM
for Automotive Applications
the three LSBs of the target address (T2, T1, T0) must
Write Scratchpad Command [0Fh]
The Write Scratchpad command applies to the data
memory and the writable addresses in the register
page. In order for the scratchpad data to be valid for
copying to the array, the user must perform a Write
Scratchpad command of 8 bytes starting at a valid row
boundary. The Write Scratchpad command accepts
invalid addresses and partial rows, but subsequent
Copy Scratchpad commands are blocked.
be equal to 000b. If T2:T0 are sent with nonzero values,
the copy function is blocked. Under certain conditions
(see the Write Scratchpad Command section) the mas-
ter 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 calculated to decide if the communication was
successful and proceed to the Copy Scratchpad com-
mand. 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-A1 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 scratchpad. 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 cor-
rectly, both flags are cleared. Now the master can con-
tinue 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 read-
ing the scratchpad.
After issuing the Write Scratchpad command, the mas-
ter must first provide the 2-byte target address, fol-
lowed by the data to be written to the scratchpad. The
data is written to the scratchpad starting at the byte off-
set of T2:T0. The ES bits E2:E0 are loaded with the
starting byte offset, and increment with each subse-
quent byte. Effectively, E2:E0 is the byte offset of the
last full byte written to the scratchpad. Only full data
bytes are accepted.
DS243-A1
When executing the Write Scratchpad command, the
CRC generator inside the DS2431-A1 (Figure 13) cal-
culates a CRC of the entire data stream, starting at the
command code and ending at the last data byte as
sent by the master. 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 (E2:E0 = 111b),
the master can send 16 read-time slots and receive the
CRC generated by the DS2431-A1.
Memory Function Commands
The Memory Function Flow Chart (Figure 7) describes
the protocols necessary for accessing the memory of
the DS2431-A1. An example on how to use these func-
tions to write to and read from the device is included at
the end of this document. The communication between
master and the DS2431-A1 takes place either at stan-
dard speed (default, OD = 0) or at overdrive speed
(OD = 1). If not explicitly set into the Overdrive mode,
the DS2431-A1 assumes standard speed.
If a Write Scratchpad is attempted to a write-protected
location, the scratchpad is loaded with the data already
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 in memory.
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