DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 24

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

There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It will affect
the functions “Read Memory with CRC”, “Copy Scratchpad”, “Clear Memory”, “Start Mission”, and “Stop Mission”.
The DS1922L/T executes the command only if the password transmitted by the master was correct or if password
checking is not enabled
Due to the special behavior of the write access logic, the Password Control Register and both passwords must be
written at the same time. When setting up new passwords, always verify (read back) the scratchpad before sending
the copy scratchpad command. After a new password is successfully copied from the scratchpad to its memory
location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the
passwords will remain in the scratchpad for public read access.
DATALOG MEMORY USAGE
Once setup for a mission, the DS1922L/T logs the temperature measurements at equidistant time points entry after
entry in its datalog memory. The datalog memory is able to store 8192 entries in 8-bit format or 4096 entries in 16-
bit format (Figure 7). In 16-bit format, the higher 8 bits of an entry are stored at the lower address. Knowing the
starting time point (Mission Time Stamp) and the interval between temperature measurements one can reconstruct
the time and date of each measurement.
There are two alternatives to the way the DS1922L/T will behave after the datalog memory is filled with data. The
user can program the device to either stop any further recording (disable “rollover”) or overwrite the previously
recorded data (enable “rollover”), one entry at a time, starting again at the beginning of the respective memory
section. The contents of the Mission Samples Counter in conjunction with the sample rate and the Mission Time
Stamp will then allow reconstructing the time points of all values stored in the datalog memory. This gives the exact
history over time for the most recent measurements taken. Earlier measurements cannot be reconstructed.
Figure 7. Temperature Logging
Temperature
8-Bit Entries
TLFS = 0
8192
ETL = 1
1000h
2FFFh
24 of 50
16-Bit Entries
Temperature
TLFS = 1
4096
ETL = 1
1000h
2FFFh
With 16-bit format,
the most-significant
byte is stored at the
lower address.
DS1922L/DS1922T