Products

RS-232 Standard

Short for recommended standard-232C, a standard interface approved by the Electronic Industries Alliance (EIA) for connecting serial devices. In 1987, the EIA released a new version of the standard and changed the name to EIA-232-D. And in 1991, the EIA teamed up with Telecommunications Industry association (TIA) and issued a new version of the standard called EIA/TIA-232-E. Many people, however, still refer to the standard as RS-232C, or just RS-232.

Almost all modems conform to the EIA-232 standard and most personal computers have an EIA-232 port for connecting a modem or other device. In addition to modems, many display screens, mice, and serial printers are designed to connect to a EIA-232 port. In EIA-232 parlance, the device that connects to the interface is called a Data Communications Equipment (DCE) and the device to which it connects (e.g., the computer) is called a Data Terminal Equipment (DTE).

Data Communications Equipment, a device that communicates with a Data Terminal Equipment (DTE) device in RS232C communications. See DTE for more information.

Data Terminal Equipment, a device that controls data flowing to or from a computer. The term is most often used in reference to serial communications defined by the RS232C standard. This standard defines the two ends of the communications channel as being a DTE and Data Communications Equipment (DCE) device. In practical terms, the DCE is usually a modem or other RS-232 device being controlled by a computer and the DTE is the computer itself, or more precisely, the computer's UART chip.

The EIA-232 standard supports two types of connectors -- a 25-pin D-type connector (DB-25) and a 9-pin D-type connector (DB-9), 8-pin RJ45 connectors are also used in common practice even though they are not a part of the official standard. The type of serial communications used by PCs requires only 9 pins so either type of connector will work equally well.

Although EIA-232 is still the most common standard for serial communication, the EIA has recently defined successors to EIA-232 called RS-422 and RS-423. The new standards are backward compatible so that RS-232 devices can connect to an RS-422 port.

Glossary of Abbreviations

CTS Clear To Send [DCE --> DTE]
DCD Data Carrier Detected [DCE --> DTE]
DCE Data Communications Equipment (eg. Modem)
DSR Data Set Ready [DCE --> DTE]
DSRS Data Signal Rate Selector [DCE --> DTE]
DTE Data Terminal Equipment (eg. computer)
DTR Data Terminal Ready [DTE --> DCE]
GND Chassis Ground
NC No Connection
rxCLK Receiver (external)
RI Ring Indicator
RTS Ready To Send [DTE --> DCE]
RxD Received Data [DCE --> DTE]
SG Signal Ground
SCTS Secondary Clear To Send [DCE --> DTE]
SDCD Secondary Data Carrier Detected [DCE --> DTE]
SRTS Secondary Ready To Send [DTE --> DCE]
SRxD Secondary Received Data [DCE --> DTE]
STxD Secondary Transmitted Data [DTE --> DTE]
TxD Transmitted Data [DTE --> DTE]

PC Serial Port Connector

DB9 Male (DTE)

CryptoCom 2000 Serial Interface

DB25 Female (DCE)

For connections between a CryptoCom modem and a PC standard commercial off the shelf cables will work as well as the cable that is included with the modem.

For connecting the CryptoCom modem to another DCE device the minimum is required:

In addition to the following cable connection between the CryptoCom and the DCE device additional configuration commands are necessary. The CryptoCom requires DTR (Data Terminal Ready) in order to communicate. Since DCE devices typically do not provide this signal you must configure the CryptoCom to "ignore" DTR in order for it to operate properly. To ignore DTR the following AT is used:

AT&D0 <cr>

Once the command to ignore DTR is entered you should write this command to memory using the AT&W command.

RS-232 Specifications

The above table is for reference only