DS1921 datasheet(39/44 Pages) DALLAS

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DS1921H/Z

39 of 44

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:

Address:

20Bh

20Ch

20Dh

Data:

2Ch

7Ch

0Ah

With only a single DS1921H/Z connected to the bus master, the communication of step 4 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

0Bh

TA1, beginning offset = 0Bh

02h

TA2, address = 020Bh

<3 data bytes>

Write 3 bytes of data to scratchpad

(Reset)

Reset pulse

(Presence)

Presence pulse

CCh

Issue Skip ROM command

AAh

Issue Read Scratchpad command

0Bh

Read TA1, beginning offset = 0Bh

02h

Read TA2, address = 020Bh

0Dh

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

<3 data bytes>

Read scratchpad data and verify

(Reset)

Reset pulse

(Presence)

Presence pulse

CCh

Issue Skip ROM command

55h

Issue Copy Scratchpad command

0Bh

02h

0Dh

TA1

TA2

(AUTHORIZATION CODE)

E/S

(Reset)

Reset pulse

(Presence)

Presence pulse

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.

DS1921 Datasheet(PDF) 39 Page - Dallas Semiconductor

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