DS1921 datasheet(38/44 Pages) DALLAS

38 / 44 page

DS1921H/Z

38 of 44

STEP 3

In this example, the rollover is disabled and the search condition is set for a high temperature only. The

mission is to start with a delay of 90 (005Ah) minutes and the alarm flags TLF, THF, and TAF are

cleared. This results in the following data to be written to the special function registers:

Address:

20Eh

20Fh

210h

211h

212h

213h

214h

Data:

02h

00h*

5Ah

00h

* Writing through address locations 20Fh to 211h is faster than accessing the Mission Start Delay

With only a single DS1921H/Z connected to the bus master, the communication of step 3 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

0Eh

TA1, beginning offset = 0Eh

02h

TA2, address = 020Eh

<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

0Eh

Read TA1, beginning offset = 0Eh

02h

Read TA2, address = 020Eh

14h

Read E/S, ending offset = 14h, 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

0Eh

02h

13h

TA1

TA2

(AUTHORIZATION CODE)

E/S

(Reset)

Reset pulse

(Presence)

Presence pulse

DS1921 Datasheet(PDF) 38 Page - Dallas Semiconductor

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