In the above, the character following the pin number means:
* rarely used
+ used only if secondary channel implemented
# used only on synchronous interfaces
also, the direction of the arrow indicates which end (DTE or DCE)
originates each signal, except for the ground lines (---). For
example, circuit 2 (TD) is originated by the DTE, and received by
the DCE. Certain of the above circuits (11, 14, 16, and 18) are
used only by (or in a different way by) Bell 208A modems.
DEFINITION OF THE MOST COMMON CIRCUITS
1 CG Chassis Ground
This circuit (also called Frame Ground) is a mechanism to
insure that the chassis of the two devices are at the same
potential, to prevent electrical shock to the operator. Note
that this circuit is not used as the reference for any of
the other voltages. This circuit is optional. If it is used,
care should be taken to not set up ground loops.
2 TD Transmit Data
This circuit is the path whereby serial data is sent from
the DTE to the DCE. This circuit must be present if data is
to travel in that direction at any time.
3 RD Receive Data
This circuit is the path whereby serial data is sent from
the DCE to the DTE. This circuit must be present if data is
to travel in that direction at any time.
4 RTS Request To Send
This circuit is the signal that indicates that the DTE
wishes to send data to the DCE (note that no such line is
available for the opposite direction, hence the DTE must
always be ready to accept data). In normal operation, the
RTS line will be OFF (logic 1 / MARK). Once the DTE has
data to send, and has determined that the channel is not
busy, it will set RTS to ON (logic 0 / SPACE), and await an
ON condition on CTS from the DCE, at which time it may then
begin sending. Once the DTE is through sending, it will
reset RTS to OFF (logic 1 / MARK). On a full-duplex or
simplex channel, this signal may be set to ON once at
initialization and left in that state. Note that some DCEs
must have an incoming RTS in order to transmit (although
this is not strictly according to the standard). In this
case, this signal must either be brought across from the
DTE, or provided by a wraparound (e.g. from DSR) locally at
the DCE end of the cable.
5 CTS Clear To Send
This circuit is the signal that indicates that the DCE is
ready to accept data from the DTE. In normal operation, the
CTS line will be in the OFF state. When the DTE asserts RTS,
the DCE will do whatever is necessary to allow data to be
sent (e.g. a modem would raise carrier, and wait until it
stabilized). At this time, the DCE would set CTS to the ON
state, which would then allow the DTE to send data. When the
RTS from the DTE returns to the OFF state, the DCE releases
the channel (e.g. a modem would drop carrier), and then set
CTS back to the OFF state. Note that a typical DTE must have
an incoming CTS before it can transmit. This signal must
either be brought over from the DCE, or provided by a
wraparound (e.g. from DTR) locally at the DTE end of the
cable.
6 DSR Data Set Ready
This circuit is the signal that informs the DTE that the DCE
is alive and well. It is normally set to the ON state by the
DCE upon power-up and left there. Note that a typical DTE
must have an incoming DSR in order to function normally.
This line must either be brought over from the DCE, or
provided by a wraparound (e.g. from DTR) locally at the DTE
end of the cable. On the DCE end of the interface, this
signal is almost always present, and may be wrapped back
around (to DTR and/or RTS) to satisfy required signals whose
normal function is not required.
7 SG Signal Ground
This circuit is the ground to which all other voltages are
relative. It must be present in any RS-232 interface.
8 DCD Data Carrier Detect
This circuit is the signal whereby the DCE informs the DTE
that it has an incoming carrier. It may be used by the DTE
to determine if the channel is idle, so that the DTE can
request it with RTS. Note that some DTEs must have an
incoming DCD before they will operate. In this case, this
signal must either be brought over from the DCE, or provided
locally by a wraparound (e.g. from DTR) locally at the DTE
end of the cable.
15 TC Transmit Clock
This circuit provides the clock for the transmitter section
of a synchronous DTE. It may or may not be running at the
same rate as the receiver clock. This circuit must be
present on synchronous interfaces.
17 RC Receiver Clock
This circuit provides the clock for the receiver section of
a synchronous DTE. It may of may not be running at the same
rate as the transmitter clock. Note that both TC and RC are
sourced by the DCE. This circuit must be present on
synchronous interfaces.
20 DTR Data Terminal Ready
This circuit provides the signal that informs the DCE that
the DTE is alive and well. It is normally set to the ON
state by the DTE at power-up and left there. Note that a
typical DCE must have an incoming DTR before it will
function normally. This signal must either be brought over
from the DTE, or provided by a wraparound (e.g. from DSR)
locally at the DCE end of the cable. On the DTE side of the
interface, this signal is almost always present, and may be
wrapped back around to other circuits (e.g. DSR, CTS and/or
DCD) to satisfy required hand-shaking signals if their
normal function is not required.
All of the above applies to interfacing a DTE device to a DCE
device. In order to interface two DTE devices, it is usually
sufficient to provide a 'flipped' cable, in which the pairs (TD,
RD), (RTS,CTS) and (DTR,DSR) have been flipped. Hence, the TD of
one DTE is connected to the RD of the other DTE, and vica versa.
It may be necessary to wrap various of the hand-shaking lines
back around from the DTR on each end in order to have both ends
work. In a similar manner, two DCE devices can be interfaced to
each other.
pin 01 - pin 01
pin 02 - pin 03
pin 03 - pin 02
pin 04 - pin 05
pin 05 - pin 04
pin 06 - pin 20
pin 20 - pin 06
ok... the above 180 lines is mostly informative.. only the last little section where i typed pin xx - pin xx is needed.. you only need to connect the give pins, and just make sure they go where they belong, and the two computers should talk to each other...
y be wrapped back
around (to DTR and/or RTS) to satisfy required signals whose
