Datasheet

DS2408
34 of 39
MASTER MODE
DATA (LSB FIRST)
COMMENTS
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
5Ah
Issue Channel-access Write command
TX
<PIO output byte>
Write byte to PIO
TX <inverted PIO output byte> Write inverted byte to PIO
(—) (—) DS2408 updates PIO status if transmission
was OK
RX AAh Read for verification (AAh = success)
(—) (—) DS2408 samples PIO pin status
RX <PIO pin status byte> Read PIO pin status
TX <PIO output byte> Write byte to PIO (next byte)
TX <inverted PIO output byte> Write inverted byte to PIO (next byte)
RX AAh Read for verification (AAh = success)
RX <PIO pin status byte> Read PIO pin status
(—) (—)
Repeat the previous 4 steps with more PIO
output data as needed in the application.
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
When using this communication example to send data to a remote microcontroller, as in Figure 17,
synchronization between the master and the remote microcontroller 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 2
Task: Read from the PIO in an endless loop.
This task is broken into the following steps:
1) Configure RSTZ as
STRB
output.
2) Verify configuration setting.
3) Read from the PIO.
With only a single DS2408 connected to the bus master, the communication is as follows:
MASTER MODE DATA (LSB FIRST) COMMENTS
Step 1 TX (Reset) Reset pulse
RX (Presence) Presence pulse
TX CCh Issue Skip ROM command
TX CCh
Issue Write Conditional Search Register
command
TX 8Dh TA1, target address = 8Dh
TX 00h TA2, target address = 008Dh