DS1921G-F5# Maxim Integrated Products, DS1921G-F5# Datasheet - Page 18

• Manufacturer Part Number: DS1921G-F5#
• Description: IBUTTON THERMOCHRON F5
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1921G-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 512B
• Memory Type: NVSRAM (Non-Volatile SRAM)
• Ic Output Type: Digital
• Sensing Accuracy Range: ± 1.3°C
• Supply Current: 10µA
• Supply Voltage Range: 2.8V To 5.25V
• Termination Type: Quick Connect
• Operating Temperature Range: -40°C To +85°C
• Supply Voltage Min: 2.8V
• Rohs Compliant: Yes
• Filter Terminals: Quick Connect
• Accuracy %: 1°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Thermochron iButton
Figure 8. Alarm Timestamps and Durations Address Map
214h). This way, if the search conditions (address
20Eh) are set accordingly, the master can quickly iden-
tify devices with temperature alarms by means of the
conditional search function (see the ROM Function
Commands section). The device also generates a time-
stamp of when the alarm occurred and begins record-
ing the duration of the alarming temperature.
Timestamps and durations where the temperature
leaves the tolerance band are stored in the address
range 0220h to 027Fh, as shown in Figure 8. This allo-
cation allows recording 24 individual alarm events and
periods (12 periods for too hot and 12 for too cold). The
date and time of each of these periods can be deter-
mined from the Mission Timestamp register and the
time distance between each temperature reading.
The alarm timestamp is a copy of the Mission Samples
Counter register when the alarm first occurred. The
least significant byte is stored at the lower address.
One address higher than the timestamp, the DS1921G
maintains a 1-byte duration counter that stores the
number of samples the temperature was found to be
beyond the threshold. If this counter has reached its
limit after 255 consecutive temperature readings and
the temperature has not yet returned to within the toler-
ance band, the device issues another timestamp at the
next higher alarm location and opens another counter
to record the duration. If the temperature returns to nor-
mal before the counter has reached its limit, the dura-
18
______________________________________________________________________________________
0224h to 0227h
0228h to 024Fh
0254h to 0257h
0258h to 027Fh
ADDRESS
0220h
0221h
0222h
0223h
0250h
0251h
0252h
0253h
Mission Samples Counter, Center Byte
Mission Samples Counter, Center Byte
Mission Samples Counter, High Byte
Mission Samples Counter, High Byte
Mission Samples Counter, Low Byte
Mission Samples Counter, Low Byte
Alarm Timestamp and Durations
Alarm Timestamp and Durations
Alarm Timestamp and Duration
Alarm Timestamp and Duration
Alarm Duration Counter
Alarm Duration Counter
DESCRIPTION
tion counter of the particular timestamp does not incre-
ment any further. Should the temperature again cross
this threshold, it is recorded at the next available alarm
location. This algorithm is implemented for the low tem-
perature thresholds as well as for the high temperature
threshold.
The typical task of the DS1921G iButton is recording
the temperature of a temperature-sensitive object.
Before the device can perform this function, it needs to
be configured. This procedure is called missioning.
First, the DS1921G must have its RTC set to a valid time
and date. This reference time can be UTC (also called
GMT, Greenwich Mean Time) or any other time stan-
dard that was chosen for the application. The clock
must be running (EOSC = 0) for at least one second.
Setting an RTC alarm is optional. The memory assigned
to store the alarm timestamps and durations, tempera-
ture histogram, Mission Timestamp, Mission Samples
Counter, Mission Start Delay, and Sample Rate must be
cleared using the Clear Memory command. In case
there were temperature alarms in the previous mission,
the TLF and THF flags need to be cleared manually. To
enable the device for a mission, the EM flag must be
set to 0. These are general settings that have to be
made regardless of the type of object to be monitored
and the duration of the mission.
High Alarms 3 to 12
Low Alarms 3 to 12
ALARM EVENT
High Alarm 1
High Alarm 2
Low Alarm 1
Low Alarm 2
Missioning