Datasheet
DS1921H/Z
36 of 45
MISSION EXAMPLE: PREPARE AND START A NEW MISSION
Assumption: The previous mission has come to an end. To end an ongoing mission write the MIP bit in
the Status Register to 0.
The preparation of a DS1921H/Z for a mission including the start of the mission requires up to four steps:
Step 1: set the RTC (if it needs to be adjusted)
Step 2: clear the data of the previous mission
Step 3: set the search condition and mission start delay, clear alarm flags
Step 4: set the temperature alarms and write the sample rate to start the mission
STEP 1
Let the actual time be 15:30:00 hours on Monday, the 1
st
of April in 2002. This results in the following
data to be written to the RTC registers:
Address:
200h
201h
202h
203h
204h
205h
206h
Data:
00h
30h
15h
01h
81h
04h
02h
With only a single DS1921H/Z connected to the bus master, the communication of step 1 is as follows:
MASTER MODE
DATA (LSB FIRST)
COMMENTS
TX
(Reset)
Reset pulse (480μs to 960µs)
RX
(Presence)
Presence pulse
TX
CCh
Issue Skip ROM command
TX
0Fh
Issue Write Scratchpad command
TX
00h
TA1, beginning offset = 00h
TX
02h
TA2, address = 0200h
TX
<7 data bytes>
Write 7 bytes of data to scratchpad
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
TX
CCh
Issue Skip ROM command
TX
AAh
Issue Read Scratchpad command
RX
00h
Read TA1, beginning offset = 00h
RX
02h
Read TA2, address = 0200h
RX
06h
Read E/S, ending offset = 6h, flags = 0h
RX
<7 data bytes>
Read scratchpad data and verify
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
TX
CCh
Issue Skip ROM command
TX
55h
Issue Copy Scratchpad command
TX
00h
TA1
TA2 (AUTHORIZATION CODE)
E/S
TX
02h
TX
06h
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse