This product is no longer available and has been replaced by: SDM-SIO1A.
SDM-SIO1 1-Channel Serial Input/Output Module
Services Available
Repair Yes
Calibration No
Free Support Yes


The SDM-SIO1 is an RS-232, RS-422, or RS-485 serial expansion module. Up to fifteen SDM-SIO1 modules may be connected to a single data logger SDM interface. This module is commonly used to interface serial sensors to a data logger. Please refer to the Compatibility information regarding which data loggers the SDM-SIO1 may be used with.

Read More

Benefits and Features

  • Expands the number of serial devices that can communicate with the data logger


Detailed Description

The SDM-SIO1 is a serial expansion module that allows a data logger to communicate with serial devices that interface using true RS-232, RS-422, or RS-485 signals. Up to fifteen SDM-SIO1 modules may be connected to a single data logger SDM interface. Remote serial devices use industry standard hardware and protocols to connect to the data logger through the SDM-SIO1 interface. When operating in the RS-232 mode, the module also provides hardware handshaking. The SDM-SIO1 Module is implemented in such a way that it looks like a built-in serial port to the user when writing programs in CRBasic. This means that all the user needs to do is define the address of the SDM-SIO1, using a rotary switch on the side of the unit. The serial port can then be used as if it were built into the data logger.



Modes of Operation
  • RS-232 (full duplex & receive only)
  • RS-485 (half and full duplex)
  • RS-422 (half and full duplex)
Data Rates 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, or 115200 bps
Data Format
  • 8, 7 bit data size
  • None, odd or even parity
  • One or two stops bits
EMC Compliance Complies with IEC 61326.
Power Supply Connection +12 V
Operating Voltage
  • 7 V (minimum)
  • 12 V (nominal)
  • 20 V (maximum)
Operating Temperature -25° to +55°C
Dimensions 5.4 x 8.0 x 2.5 cm (2.2 x 3.1 x 1.0 in.)

Current Drain

  • 70 µA (nominal)
  • 100 μA (maximum)
Active 5 to 13 mA (depending on transmit mode and connections made)


Storage Type Both transmit and receive buffers are fill and discard.
Transmit-Buffer Size 767 bytes (buffer from data logger to sensor)
Receive-Buffer Size 2047 bytes (buffer from sensor to data logger)


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR295X (retired)
CR3000 (retired) SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.
CR5000 (retired) The CR5000 operating system must be OS 6 or higher.

SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.
CR800 (retired)
CR850 (retired)
CR9000X (retired) The CR9000X operating system must be OS 6 or higher.

Additional Compatibility Information

Data Logger Considerations

The SDM-SIO1A does NOT support auto baud rate detection nor the use of the serial port for general PakBus communications.

Enclosure Considerations

The SDM-SIO1 requires a desiccated, non-condensing environment. The SDM-SIO1 has built-in keyhole flanges for mounting to the backplates of Campbell Scientific enclosures.


SDM-SIO1 v.6 (668 KB) 10-03-2013

Current firmware for the SDM-SIO1.

Note: If your version of DevConfig does not support the download of *.hex files, you will need to type in the file name directly or display it by typing *.hex and selecting the file name from the filtered list.

View Update History

Frequently Asked Questions

Number of FAQs related to SDM-SIO1: 10

Expand AllCollapse All

  1. The SDM-SIO1 has lower power biasing of its inputs and no internal termination resistors, so it operates in the lowest power state. However, this means it can quite easily detect noise on the RS-422 cable, which can, for instance, be picked up from power leads. A simple solution to this is to add 120R termination resistors at one or both ends of the cable. Although termination resistors are only normally needed on long cable runs, they are also quite effective at reducing noise.

  2. The CR5000 does not natively support communication with serial sensors; however, SDM-SIO1 modules can be added to collect data from serial sensors.

  3. The SDM-SIO1 acts as a virtual serial terminal to a CRBasic data logger. The data logger’s serial functions can be used to control the device.

  4. Yes. This feature was added in 2013. Ensure that both the data logger operating system and the SDM-SIO1 firmware are up to date. Using an SDM-SIO1, the data logger can be a Modbus client or server, although the intended and most common use is for client operation. In CRBasic, use the SerialOpen() instruction to configure the SDM-SIO1 interface and the ModBusClient() instruction to issue Modbus commands.

  5. The MD485 RS-485 Multidrop Interface is a general communication interface or serial converter. Additionally, the MD485 can be used without a data logger and offers collision avoidance for PakBus communications.

    The SDM-SIO1 Serial Input/Output Module is designed for acquiring data from smart serial sensors, rather than for general communications like data collection or program downloads. The SDM-SIO1 can operate in half- and full-duplex modes, has a smaller form factor, works with RS-422, and can be daisy-chained in quantities of up to 15 on a single three-wire SDM port.

  6. It depends. It is possible to connect serial sensors to a data logger without the use of an SDM-SIO4. However, if the sensors require hardware flow control or true RS-232 voltage levels, an SDM-SIO4 may be needed. The SDM-SIO1 also works with RS-485 signals and is a preferred alternative to the SDM-SIO4.

  7. An interface is required. This can be done using an SDM-SIO1, or a third-party RS-422 to RS-232 converter.

  8. Not the same, but similar. The SDM-SIO4 provides RS-232 voltage levels; the CR1000 control ports provide 0 to 5 V only. Both usually work with all sensors, and both devices are compatible with RS-232 and TTL logic. The CR1000 is easier to set up and program for serial input. The SDM-SIO1 is a preferred alternative to the SDM-SIO4.

    When compared to the CR10X, the CR1000 can handle strings as a specific data type. It also has more integrated serial interfaces including the following:

    • Four control port pairs—COM1 (C1 TX / C2 RX) through COM4 (C7 TX / C8 RX)
    • RS-232 port
    • CS I/O port for connection to CS I/O peripherals

    The serial I/O capabilities of the CR1000/CR3000 are similar to, and faster than, the SDM-SIO4 capabilities on a CR10X or CR23X. SDM devices are addressable and are connected to a data logger on C1 through C3. Therefore, one benefit of using multiple SDM devices on a CR1000 datalogger is that only three control ports are used.

  9. The CR1000, CR3000, and CR800-series dataloggers can be used to collect and process binary data from smart sensors via serial or TCP/IP socket connections. In some cases, a converter or communications peripheral may be required.

    Note: The capabilities mentioned above are not available for the CR200X-series, CR5000, and CR9000X dataloggers.

Case Studies

Flemish Coast: Pile Monitoring
Cofely Fabricom NV/SA (GDFSuez) has utilized Campbell Scientific equipment on numerous projects in both more

Listed Under

Other Accessory for the following products:

Privacy Policy Update

We've updated our privacy policy.  Learn More

Cookie Consent

Update your cookie preferences.  Update Cookie Preferences