DS1922E-F5# Maxim Integrated Products, DS1922E-F5# Datasheet - Page 37

• Manufacturer Part Number: DS1922E-F5#
• Description: IBUTTON TEMP LOGGER 4KBit F5
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1922E-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 512B
• Memory Type: NVSRAM (Non-Volatile SRAM)
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption

The DS1922E uses two types of CRCs. One CRC is an
8-bit type and is stored in the most significant byte of
the 64-bit ROM. The bus master can compute a CRC
value from the first 56 bits of the 64-bit ROM and com-
pare it to the value stored within the DS1922E to deter-
mine if the ROM data has been received error-free. The
equivalent polynomial function of this CRC is X
X
ed) form, and it is computed at the factory and lasered
into the ROM.
The other CRC is a 16-bit type, generated according to
the standardized CRC-16 polynomial function x
+ x
reading register pages or the data-log memory using
the Read Memory with CRC command and for fast veri-
fication of a data transfer when writing to or reading
from the scratchpad. In contrast to the 8-bit CRC, the
Figure 14. Noise Suppression Scheme
Figure 15. CRC-16 Hardware Description and Polynomial
4
+ 1. This 8-bit CRC is received in the true (noninvert-
2
X
8
+ 1. This CRC is used for error detection when
X
0
V
STAGE
PUP
V
9TH
TH
0V
STAGE
1ST
High-Temperature Logger iButton with 8KB
V
X
HY
9
X
1
______________________________________________________________________________________
STAGE
10TH
STAGE
2ND
X
10
CASE A
STAGE
11TH
CRC Generation
X
11
X
2
STAGE
12TH
STAGE
3RD
X
POLYNOMIAL = X
12
X
8
16
3
+ X
STAGE
13TH
+ x
t
t
STAGE
REH
GL
4TH
5
15
+
X
CASE B
13
16
X
+ X
4
STAGE
14TH
15
16-bit CRC is always communicated in the inverted
form. A CRC generator inside the DS1922E (Figure 15)
calculates a new 16-bit CRC as shown in the command
flowchart of Figure 9. The bus master compares the
CRC value read from the device to the one it calculates
from the data and decides whether to continue with an
operation or to reread the portion of the data with the
CRC error. With the initial pass through the Read
Memory with CRC flowchart, the 16-bit CRC value is the
result of shifting the command byte into the cleared
CRC generator, followed by the two address bytes and
the data bytes. The password is excluded from the
CRC calculation. Subsequent passes through the Read
Memory with CRC flowchart generate a 16-bit CRC that
is the result of clearing the CRC generator and then
shifting in the data bytes.
With the Write Scratchpad command, the CRC is gener-
ated by first clearing the CRC generator and then shift-
STAGE
+ X
5TH
2
+ 1
X
14
X
5
STAGE
15TH
STAGE
6TH
Data-Log Memory
X
6
STAGE
7TH
t
REH
t
GL
X
15
X
INPUT DATA
7
STAGE
CASE C
16TH
STAGE
8TH
X
16
CRC OUTPUT
37