DS1922E
iButton High-Temperature Logger with
8KB Data-Log Memory
Clear Memory with Password [96h]
The Clear Memory with Password command is used to
prepare the device for another mission. This command
is only executed if no mission is in progress. After the
command code the master must transmit the 64-bit full-
access password followed by an FFh dummy byte. If
passwords are enabled and the transmitted password
is different from the stored full-access password or a
mission is in progress, the Clear Memory with
Password command fails. The device stops communi-
cating and waits for a reset pulse. If the password was
correct or if passwords were not enabled, the device
clears the Mission Timestamp register, Mission
Samples Counter register, and all alarm flags of the
Alarm Status register. After these cells are cleared, the
MEMCLR bit of the General Status register reads 1 to
indicate the successful execution of the Clear Memory
with Password command. Clearing of the data-log
memory is not necessary because the mission samples
counter indicates how many entries in the data-log
memory are valid.
Forced Conversion [55h]
The Forced Conversion command can be used to mea-
sure the temperature without starting a mission. After
the command code, the master must send one FFh
byte to get the conversion started. The conversion
result is found as a 16-bit value in the Latest
Temperature Conversion Result register. This com-
mand is only executed if no mission is in progress (MIP
= 0). It cannot be interrupted and takes maximum
600ms to complete. During this time memory access
through the 1-Wire interface is blocked. The device
behaves the same way as during a mission when the
sampling interferes with a memory/control function
command. See the Memory Access Conflicts section
for details.
Maxim Integrated
Start Mission with Password [CCh]
The DS1922E uses a control function command to start
a mission. A new mission can only be started if the pre-
vious mission has been ended and the memory has
been cleared. After the command code, the master
must transmit the 64-bit full-access password followed
by an FFh dummy byte. If passwords are enabled and
the transmitted password is different from the stored
full-access password or a mission is in progress, the
Start Mission with Password command fails. The device
stops communicating and waits for a reset pulse. If the
password was correct or if passwords were not
enabled, the device starts a mission. If SUTA = 0, the
sampling begins as soon as the mission start delay is
over. If SUTA = 1, the first sample is written to the data-
log memory at the time the temperature alarm
occurred. However, the mission sample counter does
not increment. One sample period later, the Mission
Timestamp register is set and the regular sampling and
logging begins. While the device is waiting for a tem-
perature alarm to occur, the WFTA flag in the General
Status register reads 1. During a mission there is only
read access to the register pages.
Stop Mission with Password [33h]
The DS1922E uses a control function command to stop
a mission. Only a mission that is in progress can be
stopped. After the command code, the master must
transmit the 64-bit full-access password followed by a
FFh dummy byte. If passwords are enabled and the
transmitted password is different from the stored full-
access password or a mission is not in progress, the
Stop Mission with Password command fails. The device
stops communicating and waits for a reset pulse. If the
password was correct or if passwords were not
enabled, the device clears the MIP bit in the General
Status register and restores write access to the register
pages. The WFTA bit is not cleared. See the descrip-
tion of the General Status register for a method to clear
the WFTA bit.
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