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
Specifications |
RS-232 |
| Mode of Operation |
Single-Ended |
| Total Number of Driver/Receivers per line |
1 |
| Maximum Cable Length |
50 Ft. |
| Maximum Data Rate |
230,400 bps |
| Maximum Driver Output Voltage |
+/- 25V |
| Driver Output Signal Level (Loaded Min) |
Loaded |
+/- 5V to 15V |
| Driver Output Signal Level (Unloaded Max) |
Unloaded |
+/- 25V |
| Driver Load Impedance (Ohms) |
3K to 7K |
| Max Driver Current in High Z State |
Power On |
N/A |
| Max Driver Current in High Z State |
Power Off |
+/- 6mA @ +/-2V |
| Slew Rate (Max) |
30V/uS |
| Receiver Input Sensitivity |
+/- 15V |
| Receiver Input Voltage Range |
+/- 3V |
| Receiver Input Resistance (Ohms) |
3K to 7K |
The above table is for reference only
