DS2433+ Maxim Integrated Products, DS2433+ Datasheet - Page 19

• Manufacturer Part Number: DS2433+
• Description: IC EEPROM 4KBIT TO92-3
• Manufacturer: Maxim Integrated Products

Specifications of DS2433+

• Format - Memory: EEPROMs - Serial
• Memory Type: EEPROM
• Memory Size: 4K (256 x 16)
• Interface: 1-Wire Serial
• Operating Temperature: -40°C ~ 85°C
• Package / Case: TO-92-3 (Long Body), TO-226
• Organization: 4 K x 1
• Interface Type: 1-Wire
• Supply Voltage (max): 6 V
• Supply Voltage (min): 2.8 V
• Maximum Operating Current: 500 uA
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Speed: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

DS2433
CRC GENERATION
With the DS2433 there are two different types of CRCs (Cyclic Redundancy Checks). 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 compare it to the value stored within the DS2433 to
determine if the ROM data has been received error-free by the bus master. The equivalent polynomial
8
5
4
function of this CRC is: X
+ X
+ X
+ 1. This 8-bit CRC is received in the true (noninverted) form
when reading the ROM of the DS2433. It is computed at the factory and lasered into the ROM.
16
The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x
+
15
2
x
+x
+ 1. This CRC is used for fast verification of a data transfer when writing to the scratchpad. It is the
same type of CRC as is used with NV RAM based iButtons® for error detection within the iButton
Extended File Structure. In contrast to the 8-bit CRC, the 16-bit CRC is always returned or sent in the
complemented (inverted) form. A CRC-generator inside the DS2433 chip (Figure 12) will calculate a new
16-bit CRC as shown in the command flowchart of Figure 7. 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.
With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and then
shifting in the command code, the Target Addresses TA1 and TA2 and all the data bytes. The DS2433
will transmit this CRC only if the data bytes written to the scratchpad include scratchpad ending offset
11111b. The data may start at any location within the scratchpad.
For more details on generating CRC values including example implementations in both hardware and
software, refer to the Book of iButton Standards.
Figure 12. CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL
16
15
2
(POLYNOMIAL X
+ X
+ X
+ 1)
iButton is a registered trademark of Maxim Integrated Products, Inc.
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