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DS1990A
Serial Number iButton
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is
important that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device
attached to the 1-Wire bus must have open-drain or
three-state outputs. The 1-Wire port of the DS1990A is
open drain with an internal circuit equivalent to that
shown in Figure 4. A multidrop bus consists of a 1-Wire
bus with multiple slaves attached. At standard speed,
the 1-Wire bus has a maximum data rate of 16.3kbps.
The value of the pullup resistor primarily depends on
the network size and load conditions. For most applica-
tions, the optimal value of the pullup resistor is approxi-
mately 2.2k Ω . The idle state for the 1-Wire bus is high.
If for any reason a transaction needs to be suspended,
the bus must be left in the idle state if the transaction is
to resume. If this does not occur and the bus is left low
V PUP
SIMPLE BUS MASTER
R PUP
for more than 120μs, one or more devices on the bus
may be reset.
Transaction Sequence
The protocol for accessing the DS1990A through the
1-Wire port is as follows:
? Initialization
? ROM Function Command
Initialization
All transactions on the 1-Wire bus begin with an initial-
ization sequence. The initialization sequence consists
of a reset pulse transmitted by the bus master followed
by presence pulse(s) transmitted by the slave(s). The
presence pulse lets the bus master know that the
DS1990A is on the bus and is ready to operate. For
more details, see the 1-Wire Signaling section.
DS1990A 1-Wire PORT
Rx
Tx
OPEN-DRAIN
PORT PIN
DS2480B BUS MASTER
Rx = RECEIVE
Tx = TRANSMIT
DATA
100 Ω MOSFET
+5V
Rx
Tx
HOST CPU
V DD
V PP
POL
1-W
TO 1-Wire DATA
SERIAL
PORT
SERIAL IN
SERIAL OUT
RXD
TXD
N.C.
GND
DS2480B
Figure 4. Hardware Configuration
Maxim Integrated
5
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DS1990A-F3+C0B 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F3+C80 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F3+C8F 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F3-W 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F5 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F5# 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F5/E4F 功能描述:序列号注册 RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体:
DS1990A-F5+ 功能描述:序列号注册 Serial Number iButton RoHS:否 制造商:Maxim Integrated 数据总线宽度: 电源电压-最大: 电源电压-最小: 最大工作温度: 最小工作温度: 安装风格: 封装 / 箱体: