DB-9 to RJ-45 Null Modem

DB-9 to RJ-45 Null Modem

Post by Richard Swi » Wed, 20 Jul 1994 23:09:04

Recently I made a cable to connect from a PC running BSDI 1.1 to another
running SCO with Digicom Digiboard/16.  The connection is direct, BSDI
serial port to SCO/digiboard (8 pin RJ45) and I am having difficulty bringing
MST PPP up on the line.  The cable is 50 feet long and the pin outs are:


        RJ-45 - 8 pin           RS-232 DB-9
        Signal  pin             Signal  pin

        DCD     1               DTR     4
        RTS     2               CTS     8
        GND     3               GND     Chassis Ground
        TxD     4               RxD     2
        RxD     5               TxD     3
        SG      6               SG      5
        CTS     7               RTS     7
        DTR     8               DCD     1

I want to be able to support RTS/CTS flow control.  Is this the wiring I
should use?  

thanks in advance,


  Richard Swift                      Phoenix Systems Synectics Inc.
                  Network integration and Internet services.
        Practice random acts of kindness and senseless beauty.
  +1 613 733 0550 (voice)                     +1 613 733 2416 (Fax)


1. Creating DB-9 Female to RJ-45 Adapter

 I am putting together a Cisco POD and Im useing a 2511 as a Comm Server
with a Cab-Octal-Async cable.  I have a  NetReach Remote Power Re-boot
Switch  RPB-115  that has 1 DB-9 male DTE Configuration port for
managment.  The port(s) are pinned :

DB-9 Male                                                          RJ-45
DCD 1 --> Carrier/Send                                        RTS 8
RXD 2 --> Data In                                                 DTR 7
TXD 3 <-- Data Out                                              TXC 6
DTR 4 <-- Ready                                                   TXC GND 5
GND5                                                         `          
     RXC 3
RTS  7                                                                
   DSR 2
     CTS 1
I want to be able to reverse telnet into this device via the 2511.  If i
were to make a DB-9 Female to RJ-45 Adapter, to cross the communication
from the rolled cable to the DB-9 port of the RPB-115,  what would be
the pin-to-pin mapping?



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