Basic Comms Check

The easiest way to get started with the RockBLOCK 9603 is to use the included USB serial cable.

This cable contains an FTDI FT232R chip. You may need to install drivers, which are available here:

The RockBLOCK 9603 can not communicate with the Iridium satellites indoors. So to actually try a satellite data transfer, you'll need to somehow have the antenna obtain a view of the sky. We just placed it on an open window sill and it worked OK. If you have a laptop, that could make things easier.

Once you have the COM port showing up on your PC, use a terminal program to connect. The serial parameters are:

  • Baud Rate = 19200
  • Data Bits = 8
  • Parity = N
  • Stop Bits = 1

The examples here show using screen on a linux machine.

AT Commands

The RockBLOCK 9603 uses an AT command set that is documented here:

All commands start with AT followed by the specific command and end with a carriage return (\r). There are a lot commands, but only a few really matter. Here's a short list of the important ones:

  • +SBDIX - Initiate an Short Burst Data session, i.e. talk to the satellites. Make sure you have loaded message data first.
  • +SBDWT - Write text message into outbound buffer
  • +SBDWB - Write binary data into outbound buffer
  • +SBDRT - Read text message from inbound buffer
  • +SBDRB - Read binary data in from inbound buffer
  • +SBDSX - Status

For example, to get status, you would send:

Download: file

If you are using a terminal program, the \r is typically sent when you press the Enter key. So you don't actually type it. But when you are writing custom software to talk directly over serial, then you'll need to remember to add a \r to your data string.

Basic Info

Before we try a satellite data transfer, let's make sure the basics work. We'll use the commands +CGMI and +CGMM to obtain model information. This information comes directly from the RockBLOCK 9603 modem and does not require any satellite access.

Launch screen or whatever terminal program you are using.

Set baud rate to 19200. For screen, that's a command line parameter.

Then type AT and press Enter. You don't need to actually enter the \r.

If you get the OK response, you're talking. Then try AT+CGMI and AT+CGMM and you should get something like the info shown.

Hello World

OK, fun part time. Let's try and send a message. If you aren't already connected to the RockBLOCK, see the previous section. You also need to have your service enabled by purchasing line rental and credits.

For this initial test we'll use text. Later we'll use binary data, which is generally the way all the communication should be done. Text is just a convenience feature.

Once you are connected, type AT+SBDWT=Hello World and then press Enter.

You should receive the response OK.

To send the message, type AT+SBDIX and press Enter.

It will attempt to talk to the satellites and after a period of time return a status as +SBDIX: 32, 8, 2, 0, 0, 0.

If the first number is not 0, then the message did NOT transmit and you'll need to try again.

Keep entering the AT+SBDIX command until the first number in the status return is 0.

You may have to try this several times depending on how good your view of the sky is, where the satellites are, etc. Wait 10s of seconds between each try. Don't spam the sats, yo.

If you now log into your account and got to Messages, you should see the arrived message with "Hello World" in the payload.

There are no credits consumed for the failed attempts, so don't worry about the number of retries. Only the one final successful attempt actually deducts from your credit balance.

What Are Those Status Numbers?

The status values, the six numbers, returned from a call to AT+SBDIX are:

MO status, MOMSN, MT status, MTMSN, MT length, MT


  • MO status = status of outgoing transmission
  • MOMSN = outbound sequence number
  • MT status = status of inbound transmission
  • MTMSN = inbound sequence number
  • MT length = bytes received
  • MT queued = messages waiting to be delivered

The first one, MO status, is the most important for determining transmission success. There is a full list of possible values and their meaning in the AT Command Reference. Briefly:

  • 0 - 4 = Transmit successful
  • 32 = No network service

And for completeness:

  • MO = Mobile Originated, i.e. from the RockBLOCK
  • MT = Mobile Terminated, i.e. to the RockBLOCK
This guide was first published on Apr 08, 2020. It was last updated on Apr 08, 2020.
This page (Basic Comms Check) was last updated on Jul 03, 2020.