--- chapter.sgml.orig Sat Sep 3 14:52:36 2005 +++ chapter.sgml Sat Sep 3 20:38:56 2005 @@ -101,7 +101,7 @@ to your serial device. If you are already familiar with your hardware and the cable it requires, you can safely skip this section. - + Cables @@ -110,7 +110,7 @@ and standard (straight) RS-232 cables. The documentation for your hardware should describe the type of cable required. - + Null-modem Cables @@ -121,98 +121,359 @@ ground, straight through, but switches other signals. For example, the send data pin on one end goes to the receive data pin on the other end. - - If you like making your own cables, you can construct - a null-modem cable for use with - terminals. This table shows the RS-232C signal names and the pin - numbers on a DB-25 connector. - + You can also construct your own null-modem cable for use with + terminals (e.g., for quality purposes). This table shows the RS-232C + signal names and the pin numbers on a DB-25 connector. Note that the + standard also calls for a straight-through pin 1 to pin 1 + protective ground line, but it is often omitted. + Some terminals can get by using only pins 2, 3 and 7, while others + require different configurations than the example shown below. + + + Null-modem DB25 to DB25 cable + - - Signal - Pin # - - Pin # - Signal - + + Signal + Pin # + + Pin # + Signal + - + - - SG - 7 - connects to - 7 - SG - - - - TD - 2 - connects to - 3 - RD - - - - RD - 3 - connects to - 2 - TD - - - - RTS - 4 - connects to - 5 - CTS - - - - CTS - 5 - connects to - 4 - RTS - - - - DTR - 20 - connects to - 6 - DSR - - - - DCD - 8 - - 6 - DSR - - - - DSR - 6 - connects to - 20 - DTR - + + SG + 7 + connects to + 7 + SG + + + + TD + 2 + connects to + 3 + RD + + + + RD + 3 + connects to + 2 + TD + + + + RTS + 4 + connects to + 5 + CTS + + + + CTS + 5 + connects to + 4 + RTS + + + + DTR + 20 + connects to + 6 + DSR + + + + DTR + 20 + connects to + 8 + DCD + + + + DTR + 6 + connects to + 20 + DTR + + + + DSR + 6 + connects to + 20 + DTR + - - +
+ + Here are two other design schemes more common nowadays, + showing the RS-232C signal names and pin numbers for a DB-9 + connector and DB-9 to DB-25 connector. + + + Null-modem DB9 to DB9 cable + + + + + Signal + Pin # + + Pin # + Signal + + + + + + RD + 2 + connects to + 3 + TD + + + + TD + 3 + connects to + 2 + RD + + + + DTR + 4 + connects to + 6 + DSR + + + + DTR + 4 + connects to + 1 + DCD + + + + SG + 5 + connects to + 5 + SG + + + + DSR + 6 + connects to + 4 + DTR + + + + DCD + 1 + connects to + 4 + DTR + + + + RTS + 7 + connects to + 8 + CTS + + + + CTS + 8 + connects to + 7 + RTS + + + +
+ + + Null-modem DB9 to DB25 cable + + + + + Signal + Pin # + + Pin # + Signal + + + + + + RD + 2 + connects to + 2 + TD + + + + TD + 3 + connects to + 3 + RD + + + + DTR + 4 + connects to + 6 + DSR + + + + DTR + 4 + connects to + 8 + DCD + + + + SG + 5 + connects to + 7 + SG + + + + DSR + 6 + connects to + 20 + DTR + + + + DCD + 1 + connects to + 20 + DTR + + + + RTS + 7 + connects to + 5 + CTS + + + + CTS + 8 + connects to + 4 + RTS + + + +
+ Connect Data Set Ready (DSR) and Data Carrier Detect (DCD) internally in the connector hood, and then to Data Terminal - Ready (DTR) in the remote hood. + Ready (DTR) in the remote hood. + + The proposed design seems to be the most popular. In one + variation (explained in the book RS-232 Made + Easy, ISBN: 0137498543) the note doesn't apply + and at each end pins 4 and 5 connect only to each other + and to pin 8 at the other end. + + The correspondance between acronyms used and signal names + follow. + + + Signal acronyms + + + + + Acronyms + Signal names + + + + + + RD + Receive Data + + + + TD + Transmit Data + + + + DTR + Data Terminal Ready + + + + DSR + Data Set Ready + + + + DCD + Data Carrier Detect + + + + SG + System Ground + + + + RTS + Request to Send + + + + CTS + Clear to Send + + + +