DS1921G_11 MAXIM [Maxim Integrated Products], DS1921G_11 Datasheet - Page 16

• Manufacturer Part Number: DS1921G_11
• Description: Logs Up to 2048 Consecutive Temperature Thermochron iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

Thermochron iButton
The Mission Timestamp register indicates the time and
date of the first temperature conversion of a mission.
Subsequent temperature conversions take place as
many minutes apart from each other as specified by the
value in the Sample Rate register. Mission samples
occur on minute boundaries.
The Mission Samples Counter register indicates how
many temperature measurements have taken place
during the current mission in progress (if MIP = 1) or
during the latest mission (if MIP = 0). The value is
stored as an unsigned 24-bit integer number. This
counter is reset through the Clear Memory command.
The Device Samples Counter register indicates how
many temperature measurements have taken place
since the device was assembled at the factory. The
value is stored as an unsigned, 24-bit integer number.
The maximum number that can be represented in this
format is 16,777,215, which is higher than the expected
lifetime of the DS1921G iButton. This counter cannot be
reset under software control.
16
ADDRESS
ADDRESS
ADDRESS
021Ch
021Dh
0215h
0216h
0217h
0218h
0219h
021Ah
021Bh
021Eh
021Fh
______________________________________________________________________________________
BIT 7
BIT 7
BIT 7
0
0
0
0
Mission Samples Counter
Device Samples Counter
12/24
BIT 6
BIT 6
BIT 6
Mission Timestamp
0
0
10 Years
10 Minutes
20 Hour
AM/PM
BIT 5
BIT 5
BIT 5
0
10 Date
10 Months
10 Hour
BIT 4
BIT 4
BIT 4
Center Byte
Center Byte
High Byte
High Byte
Once set up for a mission, the DS1921G logs the tem-
perature measurements simultaneously byte after byte
in the data-log memory as well as in histogram form in
the histogram memory. The data-log memory is able to
store 2,048 temperature values measured at equidis-
tant time points. The first temperature value of a mission
is written to address location 1000h of the data-log
memory, the second value to address location 1001h
and so on. Knowing the starting time point (Mission
Timestamp register), the interval between temperature
measurements, the Mission Samples Counter register,
and the rollover setting, one can reconstruct the time
and date of each measurement stored in the data log.
There are two alternatives to the way the DS1921G
behaves after the 2048 bytes of data-log memory is
filled with data. With rollover disabled (RO = 0), the
device fills the data-log memory with the first 2048 mis-
sion samples. Additional mission samples are not
logged in the data-log, but the histogram and tempera-
ture alarm RAM continue to update. With rollover
enabled (RO = 1), the data log wraps around and over-
writes previous data starting at 1000h for the every
2049th mission sample. In this mode, the device stores
the last 2048 mission samples.
Low Byte
Low Byte
Mission Samples Counter Register Map
Device Samples Counter Register Map
Temperature Logging and Histogram
BIT 3
BIT 3
BIT 3
Mission Timestamp Register Map
BIT 2
BIT 2
BIT 2
Single Minutes
Single Months
Single Hours
Single Years
Single Date
BIT 1
BIT 1
BIT 1
BIT 0
BIT 0
BIT 0