DS_USB_RS485_CABLES 查看數據表（PDF） - Unspecified

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DS_USB_RS485_CABLES

USB to RS485 Serial Converter Cable

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Document Reference No.: FT_000117

USB TO RS485 SERIAL CONVERTER CABLE Datasheet

Version 1.4

Clearance No.: FTDI #75

Parameter Description

Minimum Typical Maximum Units

Conditions

Receiver Input

Common-mode input

VCM

-7

voltage range

+12

V

IN

Input Current

1.0

–0.8

VIN = +12V

mA

VIN = –7V

VTH

DIfferential Threshold

Voltage,VTH

-0.2

+0.2

V

VIHYST Input Hysteresis

20

mV

RIN

Input Resistance, RIN

12

15

kΩ

Transmitter Output

DIfferential Output Voltage,

VOD

1.5

dVOD

5

V

With RL = 54Ω. CL = 50pF *

Table 5.3 USB-RS485-WE I/O Pin Characteristics

* - The 54 ohms is the equivalent of two 120 ohm termination resistors placed on each side of the

transmission line and the input impedance of 32 receivers on the line.

Description

Conditions

ESD HBM

RS-485 Inputs and

Outputs

EN61000-4-2ContactDischarge

RS-485 Inputs and

Outputs

EN61000-4-2AirGapDischarge

RS-485 Inputs and

Outputs

Table 5.4 USB-RS485-WE ESD Tolerance

Minimum

Typical

±15 kV

±8 kV

±15 kV

Maximum

5.4 Local Echo

RS485 systems often have local echo enabled. This means any data transmitted by a device is echoed

back to itself.

The USB-RS485-WE cable allows for local echo to be enabled/disabled by changing a bit in the FT232R

EEPROM. If CBUS4 in the EEPROM is set for “PWRON#” local echo is enabled. If CBUS4 in the EEPROM is

set for “TXDEN” local echo is disabled.

Users can set this with MPROG from www.ftdichip.com

The default for the local echo is disabled (CBUS4 set for “TXDEN).

Copyright © 2010 Future Technology Devices International Limited

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