DS2408S+ Maxim Integrated Products, DS2408S+ Datasheet - Page 7

• Manufacturer Part Number: DS2408S+
• Description: PROM 1-Wire 8-Ch Addressable Switch
• Manufacturer: Maxim Integrated Products

Specifications of DS2408S+

• Lead Free Status / Rohs Status: Details

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.
The shift register bits are initialized to 0. Then, starting with the least significant bit of the family code,
one bit at a time is shifted in. After the eighth bit of the family code has been entered, the serial number is
entered. After the serial number has been entered, the shift register contains the CRC value. Shifting in
the eight bits of CRC returns the shift register to all 0s.
Figure 4. 1-Wire CRC GENERATOR
REGISTER ACCESS
The registers needed to operate the DS2408 are organized as a Register Page, as shown in Figure 5. All
registers are volatile, i. e., they lose their state when the device is powered down. PIO, Conditional
Search, and Control/Status registers are read/written using the device level Read PIO Registers and Write
Conditional Search Register commands described in subsequent sections and Figure 8 of this document.
X
MSB
MSB
0
STAGE
CRC CODE
1
st
8-BIT
X
1
STAGE
LSB
2
nd
X
MSB
2
STAGE
3
rd
CC
X
pin should be connected to the external voltage supply.
3
STAGE
POLYNOMIAL = X
4
th
48-BIT SERIAL NUMBER
7 of 36
8
X
4
+ X
STAGE
5
5
th
8
+ X
+ X
4
+ 1
5
+ X
4
+ 1. Additional information about the
LSB
X
5
STAGE
6
th
MSB
8-BIT FAMILY
INPUT DATA
CODE (29h)
X
6
STAGE
7
th
LSB
LSB
X
7
STAGE
8
th
X
8