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參數資料
| 型號： | ADM1485 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | +-5 V Low Power EIA RS-485 Transceiver |
| 中文描述： | -5 V低功耗環境影響評估的RS - 485收發器 |
| 文件頁數： | 7/8頁 |
| 文件大小： | 139K |
| 代理商： | ADM1485 |
ADM1485
REV. A
–7–
APPLICATIONS INFORMATION
Differential Data Transmission
Differential data transmission is used to reliably transmit data at
high rates over long distances and through noisy environments.
Differential transmission nullifies the effects of ground shifts and
noise signals which appear as common-mode voltages on the
line. There are two main standards approved by the Electronics
Industries Association (EIA) which specify the electrical charac-
teristics of transceivers used in differential data transmission.
The RS-422 standard specifies data rates up to 10 MBaud and
line lengths up to 4000 ft. A single driver can drive a transmis-
sion line with up to 10 receivers.
In order to cater for true multipoint communications, the
RS-485 standard was defined. This standard meets or exceeds
all the requirements of RS-422 but also allows for up to 32
drivers and 32 receivers to be connected to a single bus. An
extended common-mode range of –7 V to +12 V is defined. The
most significant difference between RS-422 and RS-485 is the
fact that the drivers may be disabled thereby allowing more than
one (32 in fact) to be connected to a single line. Only one driver
should be enabled at time, but the RS-485 standard contains
additional specifications to guarantee device safety in the event
of line contention.
Cable and Data Rate
The transmission line of choice for RS-485 communications is a
twisted pair. Twisted pair cable tends to cancel common-mode
noise and also causes cancellation of the magnetic fields gener-
ated by the current flowing through each wire, thereby, reducing
the effective inductance of the pair.
The ADM1485 is designed for bidirectional data communica-
tions on multipoint transmission lines. A typical application
showing a multipoint transmission network is illustrated in
Figure 26. An RS-485 transmission line can have as many as 32
transceivers on the bus. Only one driver can transmit at a par-
ticular time but multiple receivers may be enabled simultaneously.
As with any transmission line, it is important that reflections are
minimized. This may be achieved by terminating the extreme
ends of the line using resistors equal to the characteristic im-
pedance of the line. Stub lengths of the main line should also be
kept as short as possible. A properly terminated transmission
line appears purely resistive to the driver.
Thermal Shutdown
The ADM1485 contains thermal shutdown circuitry which
protects the part from excessive power dissipation during fault
conditions. Shorting the driver outputs to a low impedance
source can result in high driver currents. The thermal sensing
circuitry detects the increase in die temperature and disables the
driver outputs. The thermal sensing circuitry is designed to
disable the driver outputs when a die temperature of 150
°
C is
reached. As the device cools, the drivers are re-enabled at
140
°
C.
Propagation Delay
The ADM1485 features very low propagation delay ensuring
maximum baud rate operation. The driver is well balanced
ensuring distortion free transmission.
Another important specification is a measure of the skew be-
tween the complementary outputs. Excessive skew impairs the
noise immunity of the system and increases the amount of elec-
tromagnetic interference (EMI).
Receiver Open-Circuit Fail Safe
The receiver input includes a fail-safe feature which guarantees
a logic high on the receiver when the inputs are open circuit or
floating.
Table III. Comparison of RS-422 and RS-485 Interface Standards
Specification
RS-422
RS-485
Transmission Type
Maximum Cable Length
Minimum Driver Output Voltage
Driver Load Impedance
Receiver Input Resistance
Receiver Input Sensitivity
Receiver Input Voltage Range
No of Drivers/Receivers Per Line
Differential
4000 ft.
±
2 V
100
4 k
min
±
200 mV
–7 V to +7 V
1/10
Differential
4000 ft.
±
1.5 V
54
12 k
min
±
200 mV
–7 V to +12 V
32/32
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| ADM1485AR | +-5 V Low Power EIA RS-485 Transceiver |
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相關代理商/技術參數 |
參數描述 |
|---|---|
| ADM1485_12 | 制造商:AD 制造商全稱:Analog Devices 功能描述:5 V Low Power EIA RS-485 Transceiver |
| ADM1485AN | 制造商:Analog Devices 功能描述:Single Transmitter/Receiver RS-422/RS-485 8-Pin PDIP 制造商:Rochester Electronics LLC 功能描述:RS-485 HIGH SPEED I/F TX. - Bulk 制造商:Analog Devices 功能描述:Transceiver IC Transceiver Type:Differen |
| ADM1485ANZ | 功能描述:IC TXRX RS-485 HS 5V 8-DIP RoHS:是 類別:集成電路 (IC) >> 接口 - 驅動器，接收器，收發器 系列:- 產品培訓模塊:RS-232 & USB Transceiver 標準包裝:2,000 系列:- 類型:收發器 驅動器/接收器數:1/1 規程:RS232 電源電壓:3 V ~ 5.5 V 安裝類型:表面貼裝 封裝/外殼:16-SSOP（0.209"，5.30mm 寬） 供應商設備封裝:16-SSOP 包裝:帶卷 (TR) 其它名稱:296-19849-2 |
| ADM1485AQ | 制造商:AD 制造商全稱:Analog Devices 功能描述:+-5 V Low Power EIA RS-485 Transceiver |
| ADM1485AR | 制造商:Rochester Electronics LLC 功能描述:RS-485 HIGH SPEED I/F TX. - Bulk 制造商:Analog Devices 功能描述:BUS TRANSCEIVER RS485 1485 SOIC8 |
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