DS2406

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PARASITE POWER

The DS2406 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 off

of this “parasite” power source until the 1-Wire bus returns high to replenish the parasite (capacitor)

supply. In applications where the device may be temporarily disconnected from the 1-Wire bus or where

supply to maintain the device status.

When writing to the EPROM memory, the 1-Wire communication occurs at normal voltage levels and

then is pulsed momentarily to the programming voltage to cause the selected EPROM bits to be

programmed. The bus master must be able to provide 12V and 10mA to adequately program the EPROM

portions of the device. During programming, only EPROM-based devices are allowed to be present on

the 1-Wire bus.

64-BIT LASERED ROM

Each DS2406 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 8 bits are a CRC of the first 56 bits. (See Figure 3).

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

8

+ X

5

+ X

4

+ 1. Additional information about the Dallas 1-

Wire Cyclic Redundancy Check is available in Application Note 27. The shift register bits are initialized

to zero. Then starting with the least significant bit of the family code, 1 bit at a time is shifted in. After the

8th bit of the family code has been entered, then the serial number is entered. After the 48th bit of the

serial number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC

should return the shift register to all zeros. The 64-bit ROM and the 1-Wire Function Control section

allow the DS2406 to operate as a 1-Wire device and follow the protocol detailed in the section “1-Wire

Bus System”.

64-BIT LASERED ROM Figure 3

MSB

LSB

8-Bit CRC Code

48-Bit Serial Number

8-Bit Family Code (12h)

MSB

LSB MSB

LSB MSB

LSB

1-WIRE CRC GENERATOR Figure 4

R

8TH

STAGE

7TH

STAGE

6TH

STAGE

5TH

STAGE

4TH

STAGE

3RD

STAGE

2ND

STAGE

1ST

STAGE

S

INPUT DATA