DS2422 Maxim, DS2422 Datasheet - Page 33

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

DS2422
CLEAR MEMORY WITH PASSWORD [96h]
The Clear Memory with Password command is used to prepare the device for another mission. This command will
only be executed if no mission is in progress. 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 differ-
ent from the stored full-access password or a mission is in progress, the Clear Memory with Password command
will fail. The device will stop communicating and will wait for a reset pulse. If the password was correct or if
passwords were not enabled, the device will clear the Mission Time Stamp, Mission Samples Counter, Sample
Rate Register, and all alarm flags of the Alarm Status Register. After these cells are cleared, the MEMCLR bit of
the General Status Register will read 1 to indicate the successful execution of the Clear Memory with Password
command. Clearing of the datalog memory is not necessary because the Mission Samples Counter indicates how
many entries in the datalog memory are valid.
FORCED CONVERSION [55h]
The Forced Conversion command can be used to measure the temperature and read data from the serial data
interface without starting a mission. After the command code the master has to send one FFh byte to get the
conversion started. The conversion result is found as 16-bit value in the Latest Temperature Conversion Result and
Latest Serial Data Reading registers. This command is only executed if no mission is in progress (MIP = 0). It
cannot be interrupted and takes maximum 666 ms to complete. During this time memory access through the 1-
Wire interface is blocked. The device will behave the same way as during a mission when the sampling interferes
with a memory/control function command. See Memory Access Conflicts for details.
START MISSION WITH PASSWORD [CCh]
The DS2422 uses a control function command 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 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 in progress, the Start Mission with
Password command will fail. The device will stop communicating and will wait for a reset pulse. If the password
was correct or if passwords were not enabled, the device will start 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 temperature alarm to occur, the WFTA flag in the general status register will read 1. During a mission
there is only read access to the Register Pages.
STOP MISSION WITH PASSWORD [33h]
The DS2422 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 will fail. The device will stop
communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the
device will clear the MIP bit in the General Status Register and restore 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.
MEMORY ACCESS CONFLICTS
While a mission is in progress or while the device is waiting for a temperature alarm to start a mission, periodically
a temperature sample is taken and/or data is read from the serial interface and logged. This "internal activity" has
priority over 1-Wire communication. As a consequence, device-specific commands (excluding ROM function
commands and 1-Wire reset) will not perform properly when internal and "external" activities interfere with each
other. Not affected are the commands Start Mission, Forced Conversion and Clear Memory, because they are not
applicable while a mission is in progress or while the device is waiting for a temperature alarm. The table below
explains how the remaining five commands are affected by internal activity, how to detect this interference and how
to work around it.
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