DS1921H/Z
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:
Data:
20Eh
02h
20Fh
00h*
210h
00h*
211h
00h*
212h
5Ah
213h
00h
214h
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)
(Reset)
(Presence)
CCh
COMMENTS
TX
RX
TX
TX
TX
TX
TX
TX
RX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
TX
RX
Reset pulse (480µs to 960µs)
Presence pulse
Issue Skip ROM command
Issue Write Scratchpad command
TA1, beginning offset = 0Eh
TA2, address = 020Eh
0Fh
0Eh
02h
<7 data bytes>
(Reset)
(Presence)
CCh
Write 7 bytes of data to scratchpad
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Read Scratchpad command
Read TA1, beginning offset = 0Eh
Read TA2, address = 020Eh
Read E/S, ending offset = 14h, flags = 0h
Read scratchpad data and verify
Reset pulse
AAh
0Eh
02h
14h
<7 data bytes>
(Reset)
(Presence)
CCh
Presence pulse
Issue Skip ROM command
Issue Copy Scratchpad command
TA1
55h
0Eh
TA2
E/S
(AUTHORIZATION CODE)
02h
13h
(Reset)
(Presence)
Reset pulse
Presence pulse
38 of 44
DALLAS [ DALLAS SEMICONDUCTOR ]
