RS-232/422/485 Serial Communication USB Data Acquisition (DAQ) Products

ACCES I/O Products USB to Serial devices are designed for use with any computer system equipped with a USB port. Simply install the included software and connect the unit to your USB port and transform it into asynchronous serial ports for communication with serial instruments. 1, 2, and 4-port models are available offering users the choice of selectable RS-232, RS-422, or RS-485 protocols per port. All units include a rugged steel enclosure with attractive powder coat finish and anti-skid bottom and options for DIN-rail mounting and extended temperature.

Multiple peripherals such as POS, barcode scanners, scales, date-entry terminals, data acquisition modules, and automation equipment can now be recognized and used on a single USB port. It is now easier than ever to add serial ports and serial devices to any application with the trouble-free plug-and-play and hot-swapping features USB provides.

RS-485 and RS-422 have significant advantages over RS-232 as they use differential drivers instead of driving just one wire. This allows the cables in RS-485 and RS-422 applications to be up to 4000 feet, where RS-232 has a limit of 50 feet. See the table below for a comparison of cable length vs. baud rates.

Serial Communication USB Products
USB-232-INDRugged, extended temperature, single USB to RS-232 serial port adapter
USB-422-INDRugged, extended temperature, single USB to RS-422 serial port adapter
USB-485-INDRugged, extended temperature, single USB to RS-485 serial port adapter
USB-COM-2SMTwo-port USB to serial RS-232/422/485 adapter
USB-COM232-4AFour-Port USB to serial RS-232 adapter
USB-FLEXCOM4Four-Port USB to Serial RS-232/422/485 adapter
USB-IIRO4-2SMTwo-Port USB to Serial RS-232/422/485 adapter with 4 electromechanical relays and 4 optically isolated inputs.

Baud Rate vs Cable Length*
Baud Rate Standard Divisor Divisor x4 Divisor x8 Maximum Differential Cable Length*
921600 - - 1 250 ft.
460800 - 1 2 500 ft.
230400 - 2 4 1400 ft.
153600 - 3 6 2500 ft.
115200 1 4 8 3000 ft.
57600 2 8 16 4000 ft.
38400 3 12 24 4000 ft.
28800 4 16 32 4000 ft.
19200 6 24 48 4000 ft.
14400 8 32 64 4000 ft.
9600 12 48 96 4000 ft.
4800 24 96 192 4000 ft.
2400 48 192 384 4000 ft.
1200 96 384 768 4000 ft.
*These are theoretical maximums based on typical conditions and good quality cables based on the EIA 485 and EIA 422 standard for balanced differential drivers.

Acquisition, Control, Communication: Engineering and Systems

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