I'm trying to use a modem with an Apple MacBook Pro running Sierra (10.12.6) and I've been given the following instructions:

The user will have to create a standard 19200bps modem on 
the COM port used by the Iridium device with extra 
initialization command as: AT+CBST=71,0,1

But don't know where to configure this. I have a phone attached via USB that I can use to dial and connect to an ISP, but can't find anywhere to configure the AT command set.

  • I'm on version 10.12.6 – mankoff Mar 15 '18 at 13:27

You have two options to "talk" to your modem on serial ports on macOS:

  • Minicom
  • Screen

Screen is built in, and minicom is 3rd party. Before using either of the tools, you will need to know the device your modem is attached to. It will be listed in /dev/ttySX where X is the number of the actual device (most likely /dev/ttyS0). Verify for your machine.

Using Minicom

Minicom is a small, free communications program that's been around for decades and is quite solid. I personally prefer it over screen.

This assumes you've already installed the Homebrew or MacPorts software.

It's a simple ANSI graphic interface that will allow you to set your serial device, flow control, port speed etc.

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Once you have it set, you will be connected to the device on your serial port you can then send your AT commands to your modem by typing AT+CBST=71,0,1

enter image description here

Using Screen

You can use the built in screen to issue the commands (though admittedly, I am not very familiar with the utility as I favor Minicom)

You can connect to your device by issuing the command (assuming your modem/serial port is configured to 115200bps, 8 data bits, no parity bit and 1 stop bit or more commonly known "115200 8N1"):

screen /dev/ttySX 115200,cs8,-parenb,-cstopb,-hupcl

Where /dev/ttySX is the serial device connected to your modem as before. This example sets the comport to 15200 8N1.

And just like in the Minicom example, once connected, just send your AT commands to the modem.


An easy method using the graphical user interface instead of a Terminal-based program such as minicom, is to use the program "Serial"1 from the Mac App Store. You can try it for free, which is probably enough for you to a one time initialization like you indicate.

The program makes it easy for you by having a graphical user interface, where you are presented with a list of serial devices, so that you do not have to figure out which /dev/ device node your USB device is attached to.

Another option is CuteCom2 which is also graphical, but much more bare bones. However it is also free.

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