DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 33

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

DS1922L/DS1922T
READ MEMORY WITH PASSWORD AND CRC [69H]
The Read Memory with CRC command is the general function to read from the device. This command generates
and transmits a 16-bit CRC following the last data byte of a memory page.
After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte
address that indicates a starting byte location. Next the master must transmit one of the 64-bit passwords. If
passwords are enabled and the transmitted password does not match one of the stored passwords, the Read
Memory with Password and CRC 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 master reads data from the DS1922L/T
beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus
master will send 16 additional read data time slots and receive the inverted 16-bit CRC. With subsequent read data
time slots the master will receive data starting at the beginning of the next memory page followed again by the
CRC for that page. This sequence will continue until the bus master resets the device. When trying to read the
passwords or memory areas that are marked as "reserved", the DS1922L/T will transmit 00h or FFh bytes
respectively. The CRC at the end of a 32-byte memory page is based on the data as it was transmitted.
With the initial pass through the Read Memory with CRC flow, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator followed by the 2 address bytes and the contents of the data
memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result
of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of
the last page is read, the bus master will receive logical 1s from the DS1922L/T until a reset pulse is issued. The
Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
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 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 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, 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 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 register. This command is only executed if no mission
is in progress (MIP = 0). It cannot be interrupted and takes maximum 600 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 section Memory Access Conflicts for details. A
forced conversion must not be attempted while the RTC oscillator is stopped. This will cause the device to
enter into an unrecoverable state.
START MISSION WITH PASSWORD [CCH]
The DS1922L/T 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 Time Stamp will be set and the regular sampling and logging begins. While the device is
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