Copyright © 2010 Future Technology Devices International Limited

8

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

VCM

Common-mode input

voltage range

-7

+12

V

IN

Input Current

1.0

mA

VIN = +12V

–0.8

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

VOD

DIfferential Output Voltage,

dVOD

1.5

5

V

With RL = 54Ω. CL = 50pF *

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

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

Description

Conditions

Minimum

Typical

Maximum

ESD HBM

RS-485 Inputs and

Outputs

±15 kV

EN61000-4-2ContactDischarge

RS-485 Inputs and

Outputs

±8 kV

EN61000-4-2AirGapDischarge

RS-485 Inputs and

Outputs

±15 kV

Table 5.4 USB-RS485-WE ESD Tolerance

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).