RS232 SIMPLEX SNIFFING - PHYSICAL LAYER --------------------------------------- Silvio Cesare -- This is the construction of an rs232 cable sniffer, that passively sniffs all TD traffic from the PC to the peripheral. Attach the sniffer cable to another PC (or the same PC with another port), and you will be able to receive TD traffic between the original PC and peripheral. The sniffer cable is basically a simplex null modem cable. The sniffing was done with a flatbed scanner that was available [hey. it turns on!]. Total cost of construction was $0. The breakout box built earlier (from a null modem cable for the ports, the connector block from a car equalizer, and the wires/soldering iron/solder from an electronics kit), plus spare RS232 cables completed the necessary components. CABLE SETUP ----------- This is more complicated than it should be, but I went with cables etc that I already owned. Hence, some extra cable are involved for male/female conversions etc. It looks complicated written down.. an image would make it very clear how it works :( PC1 -> Cable1 -> Flatbed Scanner Cable1 was a spare cable that was available --> 9pin-female -> 25pin-male -> 25pin-female The 25pin-male attached to the 25pin-female on the flatbed scanner. This leaves the spare 25pin-female for the sniffer. This cables are quite popular (at least they used to be), so that the cable from modems etc were compatable with both 9pin/25pin ports. The 25pin-female connects to a 25pin-male port on the breakout box, where I wired as a simplex null modem cable. Cable1 -> Cable2 -> BreakoutBox -> Cable3 -> PC2 Cable2 is a 25pin-male/25pin-male extention. The 25pin-female port of the breakout box, connects to Cable3 which is what I've connected back to the original PC an a spare 9pin port. Cable3 --> PC2 Cable3 --> 9pin-male -> 9pin-male -> 25pin-female RS232 PINNING ------------- This is identical to a Null modem cable, except; CTS, RTS, are not used. RD is not used. DTR -> DSR -> CD TD -> RD GRND -> GRND -- Silvio Cesare