Step 3: Set the search condition and Mission Start Delay and clear the alarm flags

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 90min (005Ah) and the alarm flags TLF, THF, and TAF are cleared. This results in the follow-

ing data to be written to the special function registers:

With only a single DS1921G connected to the bus master, the communication of step 3 is as follows:

Thermochron iButton

______________________________________________________________________________________

39

ADDRESS

20Eh

20Fh

210h

211h

212h

213h

214h

DATA

02h

00h*

00h*

00h*

5Ah

00h

00h

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

0Eh

TA1, beginning offset = 0Eh

Tx

02h

TA2, address = 020Eh

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

0Eh

Read TA1, beginning offset = 0Eh

Rx

02h

Read TA2, address = 020Eh

Rx

14h

Read E/S, ending offset = 14h, 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

0Eh

TA1

Tx

02h

TA2

Tx

13h

E/S

(AUTHORIZATION CODE)

Tx

(Reset)

Reset pulse

Rx

(Presence)

Presence pulse

*

Writing through address locations 20Fh to 211h is faster than accessing the Mission Start Delay register in a separate cycle. The

write attempt has no effect on the contents of these registers.