SDM-SIO4A 4-Channel Serial I/O Module

The SDM-SIO4A is a serial I/O expansion module for Campbell Scientific data loggers. It is designed to add four additional and individually configurable and addressable RS-232, RS-422, or RS-485 (half- or full-duplex) serial ports to an SDM-capable data logger for the purposes of interfacing with intelligent sensors, actuators, or displays.

Up to three SDM-SIO4A modules can be connected to a single data logger SDM port. The SDM-SIO4A channels behave much like a native data logger serial port and use the same familiar serial I/O commands. The SDM-SIO4A is transient and surge protected to IEC61000-4-5 level 4 on the serial port interfaces, avoiding the need for separate transient protection in most applications.

  • Easy and compact method to add up to 12 additional serial ports to an SDM-capable Campbell Scientific data logger
  • Fully compliant with the RS-232, RS-422, and RS-485 (half- and full-duplex) standards
  • Can buffer large amounts of serial sensor data between datalogger processing events
  • Supports data logger terminal "talk-through" mode, facilitating serial device testing and diagnostics
  • Includes transient and surge protection on the serial port interface, eliminating the need for separate transient protection
  • Low idle power consumption, which is ideal for battery-powered stations


Function Expands the number of serial devices that can communicate with a data logger.
Number of Channels 4
Supported Data Rates 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200 bits/s
Supported Modes of Operation
  • RS-232 (full duplex and receive only)
  • RS-485 (half and full duplex)
  • RS-422 (half and full duplex)
  • Hardware CTS/RTS flow control is supported in RS-232 mode. The handshaking lines can also be used as general purpose I/O lines.
Supported Data Format
  • In 7 bit mode with no parity, the user must ensure that the characters received by the SDM-SIO4A have a delay of at least one bit period or greater between them. This does not affect any other configuration and does not affect transmissions out of the SDM-SIO4A.
  • 8, 7 bit data size; none, odd, or even parity; one or two stops bits
Auto Baud Rate Detection Auto baud rate detection is NOT supported.
PakBus Communications Use of the serial port for general PakBus communications is not currently supported.
  • Power supply +12 V connection
  • 7 V (minimum)
  • 12 V (nominal)
  • 30 V (maximum)
Operating Temperature -40° to +70°C (standard)
Humidity 0% to 95% (non-condensing) standard
Mounting Holes Two spaced 17.78 cm (7 in.) apart
Mounting Clips Optional DIN rail mounting clips are available, which can be fitted to the base of the case.
EMC Compliance The SDM-SIO4A has been tested and shown to comply with IEC 61326. The device incorporates transient and surge protection that is designed to meet IEC61000-4-5, level 4, providing the device is adequately grounded.
Dimensions 6.4 x 15.45 x 2.2 cm (2.51 x 6.09 x 0.86 in.) excluding mounting tabs