Datasheet

DS2408
37 of 39
After all DS2408s are initialized, perform the search process below as an endless loop:
MASTER MODE
DATA (LSB FIRST)
COMMENTS
Step 4 TX (Reset) Reset pulse
RX (Presence) Presence pulse
TX ECh Issue Conditional Search ROM command
RX <2 bits>
Read 2 bits; if both bits are 1, no push button
has been pressed; in this case return to Step
4. If the bit pattern is 01 or 10 or 00, a push
button has been pressed; in this case
continue with Step 5.
Step 5 TX <1 bits>
Identify and select the LS bit of the ROM ID
of the DS2408 that has responded to the
Conditional Search.
RX <2 bits>
Read 2 bits; this relates to the next bit of the
ROM ID of the participating device(s).
TX <1 bits>
Identify and select the next bit of the ROM ID
of the DS2408 that has responded to the
Conditional Search.
(—) (—)
Repeat the previous 2 steps until one device
has been identified and accessed. (see Note
1)
TX F0h Issue Read PIO Registers command
TX 88h TA1, target address = 88h
TX 00h TA2, target address = 0000h
RX <8 data bytes>
Read register page; the data in the Activity
Latch State Register tells which button has
been pressed.
RX <2 bytes CRC16>
Read CRC16 and verify correct data
transmission.
TX (Reset) Reset pulse
RX (Presence) Presence pulse
TX A5h Issue Resume command
TX C3 Issue Reset Activity Latch command
RX AAh Read for verification (AAh = success)
(—) (—)
Now, as the device and push button are
identified and the Activity Latch is cleared,
continue at Step 4.
Note 1: For a full description of the Search Algorithm see Application Note 187.