DS1922L/DS1922T
iButton Temperature Loggers
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 communicating 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 success-
ful execution of the Clear Memory with Password com-
mand. Clearing of the data-log memory is not
necessary because the Mission Samples Counter indi-
cates 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 command
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 inter-
feres with a memory/control function command. See the
Memory Access Conflicts section for details.
34
Start Mission with Password [CCh]
The DS1922L/DS1922T use a control function com-
mand to start a mission. A new mission can only be
started if the previous mission has been ended and the
memory has been cleared. After the command code,
the master must transmit the 64-bit full-access pass-
word 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 pass-
words 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 writ-
ten to the data-log memory at the time the temperature
alarm occurred. However, the Mission Samples Counter
does not increment. One sample period later, the
Mission Timestamp register is set and the regular sam-
pling and logging begins. While the device is waiting
for a temperature 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 DS1922L/DS1922T use a control function com-
mand 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 pass-
word 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 pass-
words 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 description of the General Status register for a
method to clear the WFTA bit.
Maxim Integrated