Datasheet

DS2408
8 of 39
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
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
X
8
POLYNOMIAL =
X
8
+ X
5
+ X
4
+ 1
1
st
STAGE
2
nd
STAGE
3
rd
STAGE
4
th
STAGE
6
th
STAGE
5
th
STAGE
7
th
STAGE
8
th
STAGE
INPUT DATA
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.
Figure 5. DS2408 REGISTER ADDRESS MAP
ADDRESS RANGE ACCESS TYPE DESCRIPTION
0000h to 0087h R Undefined Data
0088h R PIO Logic State
0089h R PIO Output Latch State Register
008Ah R PIO Activity Latch State Register
008Bh R/W Conditional Search Channel Selection Mask
008Ch R/W Conditional Search Channel Polarity Selection
008Dh R/W Control/Status Register
008Eh to 008Fh R These Bytes Always Read FFh