Serial Modem (Satcom/Sigfox)

Syrus can communicate with serial modem accessories such as Sigfox Communicator or Satcom which can transmit messages to the Sigfox network or to Iridium's™ global satellite network.

General Overview

  • The way it works is that you instruct the Syrus to use it's RS232 RX & TX cables to work in modem mode
  • Connect the Sigfox or Satcom accessory to the Syrus
  • Use the apx-serial tool or Syruslang to send messages to the serial interface via the respective Sigfox or Satcom destinations


Syrus 4 Datasheet with Pinout

Serial Wiring Pinout (found in 14-pin molex on Syrus Gateway device)

Satcom Wires Signal Description Syrus Signal Syrus Wires
RX Satcom RX, connect to the Syrus orange data transmitter cable. RS232_TX
TX Satcom TX, connect to the Syrus blue data receiver cable. RS232_RX
PWR Power for the Satcom accessory, use the same power source as the Syrus +12-24V DC.
GND Satcom's ground, connect to the Syrus 4 electrical ground cable. GND


Once you have the Sigfox or Satcom accessory connected to the Syrus you can configure the serial port to modem mode with the apx-serial tool.

$ sudo apx-serial mode modem

To test the communication with the accessory, you can use the state command.

$ sudo apx-serial modem state
    "state": "connected",
    "type": "satcom",
    "id": "300234063907660",
    "signal": 5,
    "version": 15,
    "buff_size": 50,
    "buff_count": 1

Redis Interaction

To notify the connection status, the serial application publishes

serial/notification/modem/state connected

when connected, or

serial/notification/modem/state disconnected

when disconnected.

To notify an incoming message, the serial application publishes

serial/notification/modem/message "Incoming message"


Consider the amount of messages sent via satellite on your application, start with the smallest buffer size: 10, so you don't store a buffer of 100 messages before you connect the serial modem accessory.

$ sudo apx-serial modem buffer_size 10

The signal of the satcom indicates the strength of the signal where:

  • 0: No service available.
  • 1-5: Each number represents about 2 db improvement in link margin over the previous value. 1 indicates about 2 db of link margin.

Consider that the satcom requires direct visibility to the sky with no obstruction to obtain the best results.

To view satcom communication logs and ensure there's messages being sent check the following /var/log/messages

Error codes

The apx-serial modem state command might return a msg_st field, which indicates a Satcom Message Error, the possible values are:

1Initial delimiter error.
2Final delimiter error.
3Checksum error.
4Length error.
6No network coverage.
7Error sending message.
8Indicates MO session failure
10GSS reported that the call did not complete in the allowed time.
11MO message queue at the GSS is full.
12MO message has too many segments.
13GSS reported that the session did not complete.
14Invalid segment size.
15Access is denied.
16ISU has been locked and may not make SBD calls (see +CULK command).
17Gateway not responding (local session timeout).
18Connection lost (RF drop).
19Link failure (A protocol error caused termination of the call).
20..31Reserved, but indicate failure if used.
32No network service, unable to initiate call.
33Antenna fault, unable to initiate call.
34Radio is disabled, unable to initiate call (see *Rn command).
35ISU is busy, unable to initiate call.
36Try later, must wait 3 minutes since last registration.
37SBD service is temporarily disabled.
38Try later, traffic management period (see +SBDLOE command)
39..63Reserved, but indicate failure if used.
64Band violation (attempt to transmit outside permitted frequency band).
65PLL lock failure; hardware error during attempted transmit.