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DS24B33
1-Wire 4Kb EEPROM
Slave-to-Master
A read-data time slot begins like a write-one time slot.
The voltage on the data line must remain below V TL
until the read low time t RL is expired. During the t RL win-
dow, when responding with a 0, the DS24B33 starts
pulling the data line low; its internal timing generator
determines when this pulldown ends and the voltage
starts rising again. When responding with a 1, the
DS24B33 does not hold the data line low at all, and the
voltage starts rising as soon as t RL is over.
The sum of t RL + δ (rise time) on one side and the inter-
nal timing generator of the DS24B33 on the other side
define the master sampling window (t MSRMIN to
t MSRMAX ) in which the master must perform a read from
the data line. For the most reliable communication, t RL
should be as short as permissible, and the master
should read close to but no later than t MSRMAX . After
reading from the data line, the master must wait until
t SLOT is expired. This guarantees sufficient recovery
time t REC for the DS24B33 to get ready for the next time
slot. Note that t REC specified herein applies only to a
single DS24B33 attached to a 1-Wire line. For multide-
vice configurations, t REC needs to be extended to
accommodate the additional 1-Wire device input
capacitance. Alternatively, an interface that performs
active pullup during the 1-Wire recovery time such as
the DS2482-x00 or DS2480B 1-Wire line drivers can be
used.
Improved Network Behavior
(Switchpoint Hysteresis)
In a 1-Wire environment, line termination is possible
only during transients controlled by the bus master
(1-Wire driver). 1-Wire networks, therefore, are suscep-
tible to noise of various origins. Depending on the phys-
ical size and topology of the network, reflections from
end points and branch points can add up or cancel
each other to some extent. Such reflections are visible
as glitches or ringing on the 1-Wire communication line.
V PUP
Noise coupled onto the 1-Wire line from external
sources can also result in signal glitching. A glitch dur-
ing the rising edge of a time slot can cause a slave
device to lose synchronization with the master and,
consequently, result in a Search ROM command com-
ing to a dead end or cause a device-specific function
command to abort. For better performance in network
applications, the DS24B33 uses an improved 1-Wire
front-end, which makes it less sensitive to noise.
The 1-Wire front-end of the DS24B33 differs from tradi-
tional slave devices in one characteristic: There is a hys-
teresis at the low-to-high switching threshold V TH . If a
negative glitch crosses V TH but does not go below
V TH - V HY , it is not recognized (Figure 12). The hysteresis
is effective at any 1-Wire speed.
CRC Generation
The DS24B33 uses two different types of CRCs. One
CRC is an 8-bit type and is stored in the most signifi-
cant byte of the 64-bit registration number. The bus
master can compute a CRC value from the first 56 bits
of the 64-bit registration number and compare it to the
value stored within the DS24B33 to determine if the reg-
istration number has been received error-free. The
equivalent polynomial function of this CRC is X 8 + X 5 +
X 4 + 1. This 8-bit CRC is received in the true (noninvert-
ed) form. It is computed and programmed into the chip
at the factory.
The other CRC is a 16-bit type, generated according to
the standardized CRC-16 polynomial function X 16 + X 15
+ X 2 + 1. This CRC is used for fast verification of a data
transfer when writing to the scratchpad. In contrast to
the 8-bit CRC, the 16-bit CRC is always communicated
in the inverted form. A CRC generator inside the
DS24B33 (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.
With the Write 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, and all the data bytes as they were sent
V TH
0V
V HY
by the bus master. The DS24B33 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.
For more information on generating CRC values refer to
Application Note 27: Understanding and Using Cyclic
Figure 12. Hysteresis at the Low-to-High Switching Threshold
Maxim Integrated
Redundancy Checks with Maxim iButton Products.
19
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相关代理商/技术参数
DS24B33G+U
功能描述:电可擦除可编程只读存储器 1-WIRE 4KB 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
DS24B33Q+T&R
制造商:Maxim Integrated Products 功能描述:1-WIRE 4KB EEPROM - Tape and Reel 制造商:Maxim Integrated Products 功能描述:IC EEPROM 4KBIT 6TDFN 制造商:Maxim Integrated Products 功能描述:EEPROM 1-Wire 4kbit EEPROM
DS24B33Q+T&R
功能描述:电可擦除可编程只读存储器 1-Wire 4kbit 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
DS24B33Q+U
功能描述:电可擦除可编程只读存储器 1-WIRE 4KB 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
DS24B33S
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:1-Wire 4Kb EEPROM
DS24B33S R
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:1-Wire 4Kb EEPROM
DS24B33S T
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:1-Wire 4Kb EEPROM
DS24B33S TR
制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:1-Wire 4Kb EEPROM