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CCS C Compiler for Microchip PIC micros

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Make a COM1 to COM2 crossover cable

This method describes how to make a COM1 to COM2 crossover cable, without using a soldering iron.

This means that you can transmit into COM1 using a standard terminal program, and receive these same bytes into COM2.

Note: this method is only recommended to link two serial ports on the same machine, as the ground line is not attached. It also does not link the flow control lines.

Figure 1: How to make a crossover cable

What you need

  • Two RS232 extension cables
  • 2 gender changers
  • 2 bits of wire. I used standard 0.1 inch headers, as used in the millions in the electronics industry.

All these bits are available at any computer store. I purchased all these pieces from Dick Smith Electronics.

What you do

Poke the header into pins 2 and 3 of the gender bender, as shown in figure 2 below.

Figure 2: Insert the bits of wire

As shown in figure 3 below, the transmit pin 3, and the receive pin is pin 2.

Warning: Depending on which piece of equipment you're talking about, the transmit pin and receive pin changes. The PC's transmit pin transmits into the devices receive pin, and vice versa.

Figure 3: Where to insert the bits of wire

Make sure pin 2 is going to pin 3 (ie: transmit connected to receive), and pin 3 is going to pin 2 (ie: receive connected to transmit). The completed article is shown in figure 4 below. Put a slight bend on the pieces of wire to make sure that there is good electrical contact.

Figure 4: The finished article

How to test

Download Terminal from You can also download Terminal from this site. I recommend downloading it from Bray's site, as he will have the most up to date version.

As you can see, typing in COM1 is received in COM2, and vice-versa.

Figure 4: How to test the crossover cable

Other things to note

In a normal crossover cable, all the flow control lines are connected. Also, to be fair, the ground line should be connected. However, in this case it's not so bad because both COM ports are from the same computer.

This is a quick way to verifying that both COM1 and COM2 are working. If you are serious about using a crossover cable, construct a proper one.

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