Datasheet

DS1921G
With the Read Scratchpad command, the CRC is gen-
erated by first clearing the CRC generator and then
shifting in the command code, the target addresses
TA1 and TA2, the E/S byte, and the scratchpad data
starting at the target address. The DS1921G transmits
this CRC only if the reading continues through the end
of the scratchpad, regardless of the actual ending off-
set. For more information on generating CRC values
refer to Application Note 27:
Understanding and Using
Cyclic Redundancy Checks with Maxim iButton
Products.
Thermochron iButton
34 ______________________________________________________________________________________
1ST
STAGE
2ND
STAGE
3RD
STAGE
4TH
STAGE
7TH
STAGE
8TH
STAGE
6TH
STAGE
5TH
STAGE
X
0
X
1
X
2
X
3
X
4
POLYNOMIAL = X
16
+ X
15
+ X
2
+ 1
INPUT DATA
CRC OUTPUT
X
5
X
6
11TH
STAGE
12TH
STAGE
15TH
STAGE
14TH
STAGE
13TH
STAGE
X
11
X
12
9TH
STAGE
10TH
STAGE
X
9
X
10
X
13
X
14
X
7
16TH
STAGE
X
16
X
15
X
8
Figure 16. CRC-16 Hardware Description and Polynomial
Command-Specific 1-Wire Communication Protocol—Legend
SYMBOL DESCRIPTION
RST 1-Wire reset pulse generated by master
PD 1-Wire presence pulse generated by slave
Select Command and data to satisfy the ROM function protocol (Skip ROM, Search ROM, etc.)
WS Command: “Write Scratchpad”
RS Command: “Read Scratchpad”
CPS Command: “Copy Scratchpad”
RM Command: “Read Memory”
RMC Command: “Read Memory with CRC”
CM Command: “Clear Memory”
CT Command: “Convert Temperature”
TA Target Address TA1, TA2
TA-E/S Target Address TA1, TA2 with E/S byte
<data to EOS> Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh
<data to EOP> Transfer of as many data bytes as are needed to reach the end of a memory page
<data to EOM> Transfer of as many data bytes as are needed to reach the end of the data-log memory