Establishing A Connection-Using - Tandy 102 Owner's Manual

Adjusting the RS-232
The RS-232 comes in 2 comple-
mentary versions-DTE and
DCE. These 2 versions are
designed to be connected to each
other. The DTE version, for ex-
ample, uses Signal 2 co
transmit
data; the DCE uses Signal 2 to
receive
data.
The Tandy 102, like most com-
puters and terminals, uses the
DTE version; the complementary
DCE version is used by most
modems. In other words, the
Tandy 102 is actually designed to
be connected to a modem- This
is why, to connect the Tandy 102
to
most other computers, you
need a null-modem adapter.
The null-modem adapter crosses
the wires in such a way that both
computers' DTE's "think" they
are connected to DCE's, as
shown in Figure 10.1. This works
fine when connecting to most
other computers. There are,
however, some exceptions:
Some computers use a DCE,
rather than a DTE version of
the RS-232:
If this is the case,
you should not use the null-
modem adapter.
Some computers require dif-
ferent signals from the signals
that the Tandy 102 requires:
If this is the case, you need to
have a tech nician cross the wires
in the RS-232 cable in such a
way that satisfies the signal re-
quirements of both computers.
Null-Modem Adapter
Tandy 102
DTE
Other Computer
DTE
2 (send data) 2 (send data)
3 (receive data) - -
=
3 (receive data)
4 (request to send)---,
r-
4 (request to send)
5
(clear to send)
___J
t._
5
(clear to send)
6 (data set ready)
~
6 (data set ready
7 (common
groun~ ~
7 (common ground)
20 (data terminal read ) / )
~O
(data terminal ready)
Figure 10.1.
Null-Modem Adapter.
98 / Establishing a Connection-Using a Direct Cable
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