The SDM-IO16A has 16 ports that expand the digital input and/or output capability of Campbell Scientific data loggers. This module offers similar functionality to the control ports of the majority of Campbell Scientific data loggers. The SDM-IO16A was designed to replace the SDM-IO16. The SDM-IO16A is more compact in comparison and has gas-discharge tubes fitted on all inputs for improved surge protection. It is fully software-compatible but also includes an option to run in a special high-speed mode that allows pulse measurements up to 8 kHz on all channels and four times more resolution on some timing measurements.