I swiped this data from http://unix1.hials.no/~aoy/home_uk.html, it was so darn useful I was afraid it might disappear. I put it in table form from this page. (Say 'form from' 10 times rapidly.)
| 25 Pin | 9 Pin | 9 Pin | 25 Pin | |||
| FG (Frame Ground) | 1 | - | X | - | 1 | FG |
| TD (Transmit Data) | 2 | 3 | - | 2 | 3 | RD |
| RD (Receive Data) | 3 | 2 | - | 3 | 2 | TD |
| RTS (Request To Send) | 4 | 7 | - | 8 | 5 | CTS |
| CTS (Clear To Send) | 5 | 8 | - | 7 | 4 | RTS |
| SG (Signal Ground) | 7 | 5 | - | 5 | 7 | SG |
| DSR (Data Set Ready) | 6 | 6 | - | 4 | 20 | DTR |
| DTR (Data Terminal Ready) | 20 | 4 | - | 6 | 6 | DSR |
You assemble one connector from each side of the hyphens. The frame ground on the 25 pin plug is optional and should I have been told only be connected on one side of the cable. If you need Data Carrier Detect on your cable (BBS programs, Unix Getty and so on) then you should apply this patch. On a 25 pin plug you can connect pin 6 and 8 On a 9 pin plug you can connect pin 1 and 6 These connections should be made on the same side of the cable.
| DB-25 | DCE | DB-9 | |||
| 1 | AA | x | Protective Ground | ||
| 2 | TXD | 3 | BA | I | Transmitted Data |
| 3 | RXD | 2 | BB | O | Received Data |
| 4 | RTS | 7 | CA | I | Request To Send |
| 5 | CTS | 8 | CB | O | Clear To Send |
| 6 | DSR | 6 | CC | O | Data Set Ready |
| 7 | GND | 5 | AB | x | Signal Ground |
| 8 | CD | 1 | CF | O | Received Line Signal Detector |
| 9 | -- | x | Reserved for data set testing | ||
| 10 | -- | x | Reserved for data set testing | ||
| 11 | x | Unassigned | |||
| 12 | SCF | O | Secndry Rcvd Line Signl Detctr | ||
| 13 | SCB | O | Secondary Clear to Send | ||
| 14 | SBA | I | Secondary Transmitted Data | ||
| 15 | DB | O | Transmisn Signl Elemnt Timng | ||
| 16 | SBB | O | Secondary Received Data | ||
| 17 | DD | O | Receiver Signal Element Timing | ||
| 18 | x | Unassigned | |||
| 19 | SCA | I | Secondary Request to Send | ||
| 20 | DTR | 4 | CD | I | Data Terminal Ready |
| 21 | CG | O | Signal Quality Detector | ||
| 22 | 9 | CE | O | Ring Indicator | |
| 23 | CH/CI | I/O | Data Signal Rate Selector | ||
| 24 | DA | I | Transmit Signal Element Timing | ||
| 25 | x | Unassigned |