RS232 interface chips, RS422 interface chips, and RS485 interface chips are interconnection devices for the transmission of serial data. 

They are used in:

• Notebook and portable computers
• Battery-powered and handheld devices
• Communications equipment

RS232 is a serial data standard that supports point-to-point connections and provides asynchronous communication capabilities. Hardware flow control, software flow control, and parity checking are other important features.

RS422 is a serial interface that supports longer transmission distances than RS232, but provides less signal line. RS485 is compatible with the RS422 data standard and provides a 2-wire bus topology. Typically, RS485 serial interfaces are used in applications where a single controller needs to control multiple devices. 

Specifications and Features

RS232 interface chips, RS422 interface chips, and RS485 interface chips differ in terms of product specifications and features.

Some important specifications to consider are:

• Number of drivers
• Number of receivers
• Data rate
• Slew rate
• Operating temperature
• Supply voltage

Electrostatic discharge (ESD) protection is critical for equipment reliability.

Interface chips with integral slew rate circuitry minimize radio frequency interference (RFI) and eliminate the need for external capacitors.

Features for RS232 interface chips, RS422 interface chips and RS485 interface chips include low-power operation and latch-up protection.

Charge pumps are often used in low-voltage devices. Short circuit protection enables RS232, RS422 and RS485 interface chips to withstand an accidental short circuit from a conductor in the interconnecting cable to one of the package outputs. 

Logic Family and Integrated Circuit Type

RS232 interface chips, RS422 interface chips, and RS485 interface chips differ in terms of logic family and integrated circuit (IC) package type.

Examples include:

• CMOS uses a combination of p-type and n-type metal-oxide-semiconductor field effect transistors (MOSFET).
• TTL also uses transistors, but as digital switches.
• LVDS products provide low skew, differential signaling, and relatively high speeds.

IC package types for RS232 interface chips, RS422 interface chips, and RS485 interface chips include Small outline integrated circuit (SOIC) and Quad flat package (QFP).

Industry Standards

RS232 interface chips, RS422 interface chips and RS485 interface chips conform to serial data standards from the Electronics Industries Association (EIA) and the Telecommunications Industry Association (TIA).

There are different standards for RS232 interface chips (EIA/TIA-232), RS422 interface chips (EIA/TIA-422) and RS485 interface chips (EIA/TIA-485.)

The EIA also publishes Data Terminal Equipment (DTE) to Data Communications Equipment (DCE) standards that describe the electrical, mechanical and functional interface between terminals such as cathode ray tubes (CRT) and communications equipment such as modems.

Related Standards

SMD 5962-06207 - Microcircuit, digital-linear, 3 V, RS-232, receiver / transmitter tranceiver, monolithic silicon.

NTCIP 2103 - National transportation communications for its protocol - point-to-point protocol over RS-232 subnetwork profile.

SMD 5962-89615 - Microcircuit, linear, RS-485 differential bus transceiver, monlithic silicon.

SMD 5962-86721 - Microcircuit, linear, RS-422/RS-423 line driver, monolithic silicon.

References

Image Credits:

Texas Instruments High-Performance Analog | 1-Source Electronic Components