Device Attachment; Rs-232 Connection; Null Modem Function; Figure 6-1. Standard Rs-232 Connection - Sierra Wireless DART 200 CDPD Modem User Manual

6
PN1197-00 Revision 1.0

Device Attachment

RS-232 connection

The DART 200 has an RS-232 DB9 interface. If the remote device has a
similar interface, then any standard PC communications cable functions
as a connector between the two. Otherwise, refer to Data and control
interface, p. 8-14, for a discussion of the RS-232 leads and the minimum
number required for operation.
Standard RS-232 communications cables function properly for distances
up to 50 feet. If longer lengths are required, low loss RS-232 cable or
electronic cable extenders can be used; both are available from local
cable distributors or electronic catalogs.

Null modem function

The RS-232 interface specification was defined before the invention of
microcomputers. The original intent was to standardize the method that
computers and terminals used to communicate remotely over telephone
lines. The standard specification is generalized in Figure 6-1.

Figure 6-1. Standard RS-232 connection

DTE
DCE
RS-232
Computer
Modem
The RS-232 standard specified the label Data Terminal Equipment or
Data Terminating Equipment (DTE) for terminals and computers, and
the label Data Communications Equipment (DCE) for modems. The
popularization of RS-232 serial communications resulted in many
different types of equipment, besides modems, that employ the standard.
Many manufacturers expect devices to connect directly to DTE
equipment (usually, PCs). Consequently, devices are designed with a
DCE interface, so a standard RS-232 cable meets the cabling
requirements. Common usage of RS-232 is shown in Figure 6-2.
DCE
Phone RS-232
Modem
Line
DTE
Terminal