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 PORTS OPTIONS Products RS-232 RS-422 RS-485 Baud PROT CFG ADDR CFG LRG FIFO XT 104-COM232-2 2     230.4k   Jumper Yes Yes 104-COM232-4 4     230.4k   Jumper Yes Yes 104-COM232-8 8     230.4k   Jumper Yes Yes P104-COM232-8 8     460.8k   Software Yes Yes 104-COM-2S   2 2 115.2k Jumper Jumper Yes Yes 104-ICOM-2S*   2 2 115.2k Jumper Jumper Yes Yes 104-COM-2SM 2 2 2 921.6k Jumper Jumper Yes Yes 104-COM-4S   4 4 921.6k Jumper Jumper Yes Yes 104-COM-4SM 4 4 4 921.6k Jumper Jumper Yes Yes 104-COM-8S   8 8 921.6k Jumper Jumper Yes Yes 104-COM-8SM 8 8 8 921.6k Jumper Jumper Yes Yes PROT CFG = protocol configuration XT = extended temperature option * optically isolated

 

SERIAL PORTS OPTIONS Products RS-232 RS-422 RS-485 Baud PROT CFG LOW PROF LRG FIFO LPCI-COM-1S   1 1 460.8k Jumper Yes Yes PCI-ICM-1S*   1 1 460.8k Jumper   Yes PCI-ICM-2S*   2 2 460.8k Jumper   Yes PCI-422/485-2   2 2 460.8k Jumper   Yes PCI-COM-2S 2 2 2 460.8k Jumper   Yes PCI-COM232/2 2     921.6k Fixed     PCI-COM232/4 4     921.6k Fixed     LPCI-COM232-4 4     230.4k Fixed Yes   LPCI-COM-4SM 4 4 4 921.6k Jumper Yes   PCI-COM422/4   4   115.2k Fixed   Yes PCI-ICM422/4*   4   460.8k Fixed   Yes PCI-COM485/4     4 921.6k Fixed   Yes PCI-ICM485/4*     4 460.8k Fixed   Yes LPCI-COM232-8 8     230.4k Fixed Yes   LPCI-COM422-8   8   921.6k Fixed Yes Yes LPCI-COM485-8     8 921.6k Fixed Yes Yes LPCI-COM-8SM 8 8 8 921.6k Jumper Yes   PROT CFG = protocol configuration LOW PROF = low profile form factor * optically isolated

 

Single-Port RS-422/485 Serial Communications Card (ICOM is isolated)

MODEL		DESCRIPTION	RoHS
	CONV232/485	RS-232 to RS-485 Serial Communications Adapter
	CONV232/422	RS-232 to RS-422 or four-wire RS-485 Serial Communications Adapter
	USB-232, USB-422 and USB-485	Add a single RS-232, RS-422 or RS-485 serial port to any USB equipped computer
	USB-232, USB-422 and USB-485	Single USB to RS-232, RS-422 or RS-485 serial port adapter
	USB-COM-2SM	Two-port USB to serial RS-232/422/485 adapter
	USB-COM232-4	Four-port USB to serial RS-232 adapter
	USB-COM-4S	Four-port USB to serial RS-422/485 adapter
	USB-COM-4SM	Four-Port USB to Serial RS-232/422/485 adapter
	USB-COM-4SM	Four-Port Serial Communications adapter for Universal Serial Bus
	USB-IIRO4-2SM	Two-Port USB to Serial RS-232/422/485 adapter with 4 Electromechanical relays and 4 optically isolated inputs.
	eNET-232-1	Single-Port Ethernet-to-Remote RS-232 Serial Interface Device
	eNET-422-1	Single-Port Ethernet-to-Remote RS-422 Serial Interface Device
	PCM485	PCM485 PCMCIA RS-422/485 Serial Communications Card
	WDG-SIO	Watchdog Timer and RS422/485 Serial Communications Card
	WDG-2S	Watchdog Timer and Dual RS422/RS485 Serial Communications Card
	COM422/485A and ICOM 422/485A
	COM-1S	Single-Port RS-232/422/485 Serial Communications Card
	COM-2S	Two-Port, RS-232/422/485 Serial Communications Card
	ICOM-2S	Optically-Isolated, Dual-Port RS-422 and RS-485 Serial Communications Card
	COM422/4 and COM485/4	Four-Port Serial Communications Cards
COM485/8	Eight-Port Serial Communications Card

 

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.