DS1922E-F5 MAXIM [Maxim Integrated Products], DS1922E-F5 Datasheet - Page 22

• Manufacturer Part Number: DS1922E-F5
• Description: High-Temperature Logger iButton with 8KB Data-Log Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

efficiency, the target address for writing should point to
the beginning of a page, i.e., the byte offset is 0. Thus,
the full 32-byte capacity of the scratchpad is available,
resulting also in the ending offset of 1Fh. The ending
offset together with the PF flag are a means to support
the master checking the data integrity after a Write
command. The highest valued bit of the E/S register,
called authorization accepted (AA), indicates that a
valid Copy command for the scratchpad has been
received and executed. Writing data to the scratchpad
clears this flag.
To write data to the DS1922E, 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. In the next step, the master sends the
Read Scratchpad command to read the scratchpad
and to verify data integrity. As preamble to the scratch-
pad data, the DS1922E sends the requested target
address TA1 and TA2 and the contents of the E/S
Register. If the PF flag is set, data did not arrive cor-
rectly in 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 indicates that
the Write command was not recognized by the device.
If everything went correctly, both flags are cleared and
the ending offset indicates the address of the last byte
written to the scratchpad. Now the master can continue
verifying every data bit. After the master has verified
the data, it must send the Copy Scratchpad command.
This command must be followed exactly by the data of
the three address registers TA1, TA2, and E/S, as the
master has read them verifying the scratchpad. As
soon as the DS1922E has received these bytes, it
copies the data to the requested location beginning at
the target address.
High-Temperature Logger iButton with 8KB
Data-Log Memory
22
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Writing with Verification
Figure 9 shows the protocols necessary for accessing
the memory and the special function registers of the
DS1922E. An example on how to use these and other
functions to set up the DS1922E for a mission is includ-
ed in the Mission Example: Prepare and Start a New
Mission section. The communication between the mas-
ter and the DS1922E takes place either at standard
speed (default, OD = 0) or at overdrive speed (OD =
1). If not explicitly set into the Overdrive Mode the
DS1922E assumes standard speed. Internal memory
access during a mission has priority over external
access through the 1-Wire interface. This affects sever-
al commands in this section. See the Memory Access
Conflicts section for details and solutions.
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 T[4:0]. The master must send as many bytes as are
needed to reach the ending offset of 1Fh. If a data byte
is incomplete, its content is ignored and the partial byte
flag PF is set.
When executing the Write Scratchpad command, the
CRC generator inside the DS1922E calculates a CRC
of the entire data stream, starting at the command code
and ending at the last data byte sent by the master
(Figure 15). 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 as supplied by the master, and all the data bytes.
If the ending offset is 11111b, the master can send 16
read time slots and receive the inverted CRC-16 gener-
ated by the DS1922E.
Note that both register pages are write protected dur-
ing a mission. Although the Write Scratchpad com-
mand works normally at any time, the subsequent copy
scratchpad to a register page fails during a mission.
Write Scratchpad Command [0Fh]
Function Commands
Memory and Control