Serial Port Pins


Hi, I have a question about the serial connection, I am not very experienced, sorry in advanced.

I am trying to make a serial connection between a microcontroler (picaxe) and the fastrack. I need the micro to send ascii data to the fastrack.

My problem is how do I make the pin connection?. The picaxe uses just 1 pin out to send serial data by the command “serout”. But the fastrack serial port has 9 pins for the serial port. Can I connect the 1 pin out of the micro to serial in pin of the fastrack to make the connection? Or I have to connect all pins somehow?

Again sorry if it is a stupid question.


The fastrack provides a standard RS232 Modem (“DCE”) Interface - the pinout is shown in the User Guide.

I have no idea about this “PICaxe” - you will have to consult its documentation to see what it says about interfacing to RS232 devices.

RS232 devices are so common that the documentation must surely mention it if it can be done!

Note that a PC’s COM port is also an RS232 device, but it is a DTE interface - which is “opposite” to a DCE:


Ok, but 1 question about the RS232 port on the wavecom modem.

I have been reading that the pins that necesarily have to be connected are TXD (to transmit data), RXD (to receive data) and ground (0v). RTS (ready to send) and CTS (clear to send) are used by the handshaking but are not essential.

Is this ok? Can I use the serial port without using RTS and CTS?

Thank you very much


Note that TXD is the data to be transmitted over the GSM link - so it is an input to the Fastrack;
Similarly, RXD is the data to received from the GSM link - so it is an output from the Fastrack.

This is explained in one of the linke I cited before.

That’s not what it says in the Fastrack Manual, is it?

The default is that the Fastrack requires RTS and CTS - SO You would have to explicitly reconfigure this with AT+IFC

Alternatively, build a loop-back into your connector - see: viewtopic.php?f=3&t=419&p=3498&hilit=+loops+back+rts+cts#p3498

See also: viewtopic.php?f=53&t=1958&p=7277&hilit=loopback+rts+cts#p7277