DS1923
iButton Hygrochron Temperature/Humidity
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 pass-
word is different from the stored full access password
or a mission is in progress, the Clear Memory com-
mand 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 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 exe-
cution 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 and humidity 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 and Latest Humidity
Conversion Result registers. This command is only exe-
cuted if no mission is in progress (MIP = 0). It cannot
be interrupted and takes maximum 666ms 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.
34
Start Mission [with Password] [CCh]
The DS1923 uses a control function command to start a
mission. A new mission can only be started if the previ-
ous 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 command fails. The device stops communicat-
ing 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 Samples 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 temperature alarm to occur,
the WFTA flag in the General Status register reads 1.
During a mission there is only read access to the regis-
ter pages.
Stop Mission [with Password] [33h]
The DS1923 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 command fails. The device stops commu-
nicating 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 description of the gen-
eral status register for a method to clear the WFTA bit.
Maxim Integrated