Sierra Wireless DART 200 CDPD Modem - Manual (Page 87)

PN1197-00 Revision 1.0
6 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
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.
RS-232
Computer
DTE
Terminal Modem Modem
RS-232
DTE
Phone
Line
DCE DCE