DS1921 DALLAS [Dallas Semiconductor], DS1921 Datasheet - Page 39

• Manufacturer Part Number: DS1921
• Description: High-Resolution Thermochron iButton
• Manufacturer: DALLAS [Dallas Semiconductor]

STEP 4
In this example, the temperature alarms are set to 0 C for the low temperature threshold and 10 C for the
high temperature threshold, assuming it is a DS1921Z device. The sample rate is once every 10 minutes,
allowing the mission to last up to 14 days. This results in the following data to be written to the special
function registers:
With only a single DS1921H/Z connected to the bus master, the communication of step 4 is as follows:
If step 4 was successful, the MIP bit in the Status Register will be 1, the MEMCLR bit will be 0, and the
mission start delay will be counting down.
Address:
Data:
MASTER MODE
RX
RX
RX
RX
RX
RX
RX
RX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
20Bh
2Ch
20Ch
7Ch
DATA (LSB FIRST)
<3 data bytes>
<3 data bytes>
(Presence)
(Presence)
(Presence)
(Presence)
(Reset)
(Reset)
(Reset)
(Reset)
CCh
CCh
CCh
AAh
0Dh
0Dh
0Fh
0Bh
0Bh
0Bh
02h
02h
55h
02h
20Dh
0Ah
39 of 44
COMMENTS
Reset pulse (480µs to 960µs)
Presence pulse
Issue Skip ROM command
Issue Write Scratchpad command
TA1, beginning offset = 0Bh
TA2, address = 020Bh
Write 3 bytes of data to scratchpad
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Read Scratchpad command
Read TA1, beginning offset = 0Bh
Read TA2, address = 020Bh
Read E/S, ending offset = 0Dh, flags = 0h
Read scratchpad data and verify
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Copy Scratchpad command
TA1
TA2
E/S
Reset pulse
Presence pulse
(AUTHORIZATION CODE)
DS1921H/Z