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The equivalent polynomial function of this CRC is X + X + X + 1. This 8-bit CRC is received in the true
+ X
+ X + 1. This CRC is used for fast verification of a data transfer when writing to or reading from the
X
DS28EC20: 20Kb 1-Wire EEPROM
CRC GENERATION
The DS28EC20 uses two different 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
compare it to the value stored within the DS28EC20 to determine if the ROM data has been received error-free.
8 5 4
(noninverted) form. It is computed at the factory and programmed into the ROM.
The other CRC is a 16-bit type, generated according to the standardized CRC16 polynomial function
16 15 2
scratchpad and with the Extended Read Memory command. In contrast to the 8-bit CRC, the 16-bit CRC is always
communicated in the inverted form. A CRC generator inside the DS28EC20 (Figure 13) calculates a new 16-bit
CRC, as shown in the command flowchart (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 or to reread the
portion of the data with the CRC error.
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 as they were sent by the bus
master. The DS28EC20 transmits this CRC only if the data bytes written to the scratchpad include scratchpad
ending offset 11111b. The data can start at any location within the scratchpad.
With the Read 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, the E/S byte, and the scratchpad data as they were sent
by the DS28EC20 starting at the target address. The DS28EC20 transmits this CRC only if the reading continues
through the end of the scratchpad, regardless of the actual ending offset.
With the initial pass through the extended read memory flow, 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. Subsequent
passes through the extended read memory flow generate a 16-bit CRC that is the result of clearing the CRC
generator and then shifting in the data bytes. For more information on generating CRC values refer to Application
Note 27 : Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products
( www.maximintegrated.com/AN27 ).
Figure 13. CRC16 Hardware Description and Polynomial
Polynomial = X
+ X
+ X + 1
16
15
2
1
2
3
4
5
6
7
8
X
X
X
X
X
X
X
X
0
st
STAGE
nd
STAGE
1
rd
STAGE
2
th
STAGE
3
th
STAGE
4
th
STAGE
5
th
STAGE
6
th
STAGE
7
9
10
11
12
13
14
15
16
th
STAGE
th
STAGE
th
STAGE
th
STAGE
th
STAGE
th
STAGE
th
STAGE
th
STAGE
X
X
X
X
X
X
X
X
X
8
9
10
11
12
13
14
15
INPUT DATA
16
CRC
OUTPUT
24 of 27
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相关代理商/技术参数
DS28EC20-224-BB+
制造商:Maxim Integrated Products 功能描述:- Rail/Tube
DS28EC20P
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:DS28EC20_1203
DS28EC20P T
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:DS28EC20_1203
DS28EC20P+
功能描述:电可擦除可编程只读存储器 20Kb 1-Wire 电可擦除可编程只读存储器 RoHS:否 制造商:Atmel 存储容量:2 Kbit 组织:256 B x 8 数据保留:100 yr 最大时钟频率:1000 KHz 最大工作电流:6 uA 工作电源电压:1.7 V to 5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8
DS28EC20P+T
功能描述:电可擦除可编程只读存储器 20Kb 1-Wire 电可擦除可编程只读存储器 RoHS:否 制造商:Atmel 存储容量:2 Kbit 组织:256 B x 8 数据保留:100 yr 最大时钟频率:1000 KHz 最大工作电流:6 uA 工作电源电压:1.7 V to 5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8
DS28EC20P-224-BB+T
制造商:Maxim Integrated Products 功能描述:- Tape and Reel
DS28EC20Q-A5A-5A+T
制造商:Maxim Integrated Products 功能描述:20KB 1-WIRE EEPROM - Tape and Reel
DS28EC20Q-A5A-5A+W
制造商:Maxim Integrated Products 功能描述:20KB 1-WIRE EEPROM - Rail/Tube