Datasheet
DS1921H/Z
38 of 45
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*
00h*
00h*
5Ah
00h
00h
* 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.
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
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
TA2 (AUTHORIZATION CODE)
E/S
TX
02h
TX
13h
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse