DS1921H/Z
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 1st of April in 2002. This results in the following
data to be written to the RTC registers:
Address:
Data:
200h
00h
201h
30h
202h
15h
203h
01h
204h
81h
205h
04h
206h
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)
(Reset)
(Presence)
CCh
COMMENTS
TX
RX
TX
TX
TX
TX
TX
TX
RX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
TX
RX
Reset pulse (480µs to 960µs)
Presence pulse
Issue Skip ROM command
Issue Write Scratchpad command
TA1, beginning offset = 00h
TA2, address = 0200h
0Fh
00h
02h
<7 data bytes>
(Reset)
(Presence)
CCh
Write 7 bytes of data to scratchpad
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Read Scratchpad command
Read TA1, beginning offset = 00h
Read TA2, address = 0200h
Read E/S, ending offset = 6h, flags = 0h
Read scratchpad data and verify
Reset pulse
AAh
00h
02h
06h
<7 data bytes>
(Reset)
(Presence)
CCh
Presence pulse
Issue Skip ROM command
Issue Copy Scratchpad command
TA1
55h
00h
TA2
E/S
(AUTHORIZATION CODE)
02h
06h
(Reset)
(Presence)
Reset pulse
Presence pulse
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DALLAS [ DALLAS SEMICONDUCTOR ]
