DS1921 datasheet(36/44 Pages) DALLAS

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DS1921H/Z

36 of 44

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

(Reset)

Reset pulse (480µs to 960µs)

(Presence)

Presence pulse

CCh

Issue Skip ROM command

0Fh

Issue Write Scratchpad command

00h

TA1, beginning offset = 00h

02h

TA2, address = 0200h

<7 data bytes>

Write 7 bytes of data to scratchpad

(Reset)

Reset pulse

(Presence)

Presence pulse

CCh

Issue Skip ROM command

AAh

Issue Read Scratchpad command

00h

Read TA1, beginning offset = 00h

02h

Read TA2, address = 0200h

06h

Read E/S, ending offset = 6h, flags = 0h

<7 data bytes>

Read scratchpad data and verify

(Reset)

Reset pulse

(Presence)

Presence pulse

CCh

Issue Skip ROM command

55h

Issue Copy Scratchpad command

00h

02h

06h

TA1

TA2

(AUTHORIZATION CODE)

E/S

(Reset)

Reset pulse

(Presence)

Presence pulse

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