Datasheet

DS2408
35 of 39
MASTER MODE
DATA (LSB FIRST)
COMMENTS
TX 04h Write byte to Control/Status Register
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
Step 2 TX CCh Issue Skip ROM command
TX
F0h
Issue Read PIO Registers command
TX
8Dh
TA1, target address = 8Dh
TX 00h TA2, target address = 008Dh
RX
84h
Read Control/Status Register and verify
TX
(Reset)
Reset pulse
RX (Presence) Presence pulse
Step 3 TX
CCh
Issue Skip ROM command
TX
F5h
Issue Channel-access Read command
(—)
(—)
DS2408 samples PIO pin status
RX <PIO pin status byte> Read PIO pin status
(—) (—)
Repeat the previous 2 steps until the master
has received a total of 32 bytes of PIO pin
status
RX
<2 bytes CRC16>
Read CRC16
(—) (—)
PIO pin status and CRC loop can be
continued as long as the application requires.
TX (Reset) Reset pulse
RX (Presence) Presence pulse
When using this communication example to read data from a remote microcontroller, as in Figure 17,
synchronization between the remote microcontroller and the master can be maintained by transmitting
data packets that begin with a length byte and end with a CRC16. See Application Note 114, section
"UNIVERSAL DATA PACKET" for details.
Example 3
Task: Detect the specific DS2408 where the button was pressed and identify the pin to which the
pushbutton is connected. This task is broken into the following steps:
1) Configure the conditional search and verify configuration setting.
2) Switch off all channel output transistors.
3) Clear the activity latches.
4) Search until a pushbutton is pressed.
5) Identify device and pushbutton; reset activity latches.
The device has to respond to the conditional search if the activity latch of at least one of the 8 channels is
set. This requires the following setup data for the conditional search registers:
Channel Selection Mask, select all channels ⇒ FFh
Channel Polarity Selection, select logic 1 for all channels ⇒ FFh