Digital Peripherals / SDM-SIO1
This product is no longer available and has been replaced by: SDM-SIO1A. Some accessories, replacement parts, or services may still be available.
SDM-SIO1 1-Channel Serial Input/Output Module
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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 datalogger SDM interface. This module is commonly used to interface serial sensors to a datalogger. Please refer to the Compatibility information regarding which dataloggers the SDM-SIO1 may be used with.

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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)


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR211X (retired)
CR216X (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) 03-10-2013

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 Revision History

Frequently Asked Questions

Number of FAQs related to SDM-SIO1: 9

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  1. 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.

  2. 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.

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

  4. 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.

  5. The CR1000, CR3000, and CR800-series data loggers 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 data loggers.

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

  7. 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.

  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 datalogger on C1 through C3. Therefore, one benefit of using multiple SDM devices on a CR1000 datalogger is that only three control ports are used.

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