DS2408 Maxim, DS2408 Datasheet - Page 7

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

Figure 2. HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL
PARASITE POWER
The DS2408 can derive its power entirely from the 1-Wire bus by storing energy on an internal capacitor
during periods of time when the signal line is high. During low times the device continues to operate from
this “parasite” power source until the 1-Wire bus returns high to replenish the parasite (capacitor) supply.
If power is available, the V
Figure 3. 64-BIT LASERED ROM
64-BIT LASERED ROM
Each DS2408 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.
The next 48 bits are a unique serial number. The last eight bits are a CRC of the first 56 bits. See Figure 3
for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and
XOR gates as shown in Figure 4. The polynomial is X
Dallas 1-Wire Cyclic Redundancy Check is available in Application Note 27.
MSB
MSB
CRC CODE
Master
Command
Level:
8-BIT
Bus
1-Wire ROM Function
LSB
DS2408-Specific
Control Function
Commands
Commands
MSB
CC
pin should be connected to the external voltage supply.
1-Wire Net
48-BIT SERIAL NUMBER
DS2408
Available
Commands:
Read ROM
Match ROM
Search ROM
Skip ROM
Conditional Search
Overdrive Match
Overdrive Skip
Resume
Read PIO Registers
Channel Access Read
Channel Access Write
Write Conditional
Reset Activity Latches
Search Register
ROM
7 of 39
8
Codes:
+ X
Cmd.
CCh
ECh
CCh
3Ch
C3h
33h
55h
F0h
69h
A5h
F0h
F5h
5Ah
5
+ X
Devices
Other
Data Field
Affected:
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
RC-FLAG
64-BIT ROM, RC-FLAG, Port Status,
64-BIT ROM, RC-FLAG, OD-Flag
RC-FLAG, OD-Flag
RC-FLAG
PIO Registers
Port Input Latches
Port Output Latches
Conditional Search Register
Activity Latches
4
+ 1. Additional information about the
LSB
Cond. Search Settings,
MSB
8-BIT FAMILY
CODE (29h)
LSB
LSB
DS2408