DS1921H-F5# Maxim Integrated Products, DS1921H-F5# Datasheet - Page 23

• Manufacturer Part Number: DS1921H-F5#
• Description: IBUTTON THERMOCHRON F5
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1921H-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 512B
• Memory Type: NVSRAM (Non-Volatile SRAM)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Mission Start and Logging Process
The DS1921H/Z does not use a special command to start a mission. Instead, a mission is started by
writing a non-zero value to the Sample Rate Register using the Copy Scratchpad command. As shown in
Figure 11, a new mission can only be started if the previous mission has been stopped (MIP = 0), the
memory is cleared (MEMCLR = 1) and the mission is enabled (EM = 0). If the new sample rate is
different from zero, the value will be copied to the sample rate register. At the same time the MIP bit will
be set and the MEMCLR bit will be cleared to indicate that the device is on a mission. Next the Mission
Start Delay counter will start decrementing every minute until it is down to 0. Now the DS1921H/Z will
wait until the next minute boundary and start the logging process, which as its first action copies the
applicable RTC registers to the Mission Time Stamp.
MISSION START AND LOGGING PROCESS Figure 11
The Mission Start Process is invoked when the Copy Scratchpad function is used to set a new sample rate
by writing to the Sample Rate Register at address 020Dh. One minute after the start delay countdown is
over, the Logging Process begins and the Mission Start Process ends.
Next Minute Boundary
Scratchpad to Sample
DS1921 sets MIP = 1;
DS1921 Decrements
Mission Start Process
DS1921 Copies new
Start Delay Counter
DS1921 Waits Until
Sample Rate from
MEMCLR = 1
Rate Register
MEMCLR = 0
Counter = 0?
New Sample
Start Delay
Rate = 0?
MIP = 1?
MIP = 1?
EM = 0?
N
Y
Y
N
N
Y
N
Y
N
N
Y
Y
DS1921 Sets MIP = 0
DS1921 Waits
End of Process
Until Next
Boundary
Process
DS1921
Logging
Minute
23 of 45
DS1921 Waits
Y
One Sample
DS1921 Stores Temp.
Period
DS1921 Increments
at Datalog Address
Datalog Address
Address =
Datalog
1800h?
DS1921 Copies RTC to
N
DS1921 Updates His-
ples Counter, Mission
Samples Counter and
DS1921 sets Datalog
togram, Device Sam-
Mission Time Stamp
Alarm, if applicable
DS1921 Measures
N
Y
Address = 1000h
Logging Process
Temperature
End of Process
RO = 1?
MIP = 1?
DS1921 Stores Temp.
N
DS1921 Increments
at Datalog Address
Datalog Address
lower 11 bits of
Y
DS1921H/Z