DS2408 Maxim, DS2408 Datasheet - Page 35

• Manufacturer Part Number: DS2408
• Description: The DS2408 is an 8-channel, programmable I/O 1-Wire® chip
• Manufacturer: Maxim

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:
Step 2
Step 3
Channel Selection Mask, select all channels ⇒ FFh
Channel Polarity Selection, select logic 1 for all channels ⇒ FFh
MASTER MODE
(—)
(—)
(—)
TX
TX
RX
RX
RX
RX
RX
RX
TX
TX
TX
TX
TX
TX
TX
TX
<PIO pin status byte>
DATA (LSB FIRST)
<2 bytes CRC16>
(Presence)
(Presence)
(Presence)
(Reset)
(Reset)
(Reset)
CCh
CCh
8Dh
04h
F0h
00h
84h
F5h
(—)
(—)
(—)
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Write byte to Control/Status Register
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Read PIO Registers command
TA1, target address = 8Dh
TA2, target address = 008Dh
Read Control/Status Register and verify
Reset pulse
Presence pulse
Issue Skip ROM command
Issue Channel-access Read command
DS2408 samples PIO pin status
Read PIO pin status
Repeat the previous 2 steps until the master
has received a total of 32 bytes of PIO pin
status
Read CRC16
PIO pin status and CRC loop can be
continued as long as the application requires.
Reset pulse
Presence pulse
COMMENTS
DS2408