Data Acquisition

firmware can only interpret and execute the commands it receives from the host PC sothat it knows what actions to take at any point in time.The firmware performs many functions including:• Overseeing the correct operation of all peripheral hardware devices (i.e.memory card, display, keyboard)• Interpreting, checks for error, then acting on commands received via thecommunications interface or from memory cards• Sending responses to the computer via the communications interface,including any errors that occur in the communication of the command and inthe device itself• Performing the necessary data acquisition and control functions as specifiedby the programming commands received from the host PCThe firmware for a stand-alone device is often upgraded by the manufacturer to providenew features and enhancements, and in some cases, bug fixes. Where remote stand-alonedevices are operated within an RS-485 network, it is advisable that each unit runs thesame version of firmware.The revision of the firmware is often shown on the local display upon power-up of thedevice. Where this is not the case, a system command to determine the firmware revisionis usually provided.Quality manuals provided with remote stand-alone devices will include a firmwarechange history, with the revision numbers and brief description of the changes made witheach revision. This allows the user to identify problems that are consistent with a previousrevision of the software.7.6 Stand-alone logger/controller software designThe power and flexibility provided by stand-alone logger/controllers has genericallyresulted in the hardware, and consequently the firmware that controls its operation,becoming necessarily complicated. This however, does not mean that the commands usedto instruct stand-alone devices, need to be complicated. In fact, from a programmingpoint of view it is beneficial to keep the basic command and data structure simple andreadable. To this end, a simple ASCII-based command structure is commonly implemented.ASCII-based command and data response formats are popular because of theirsimplicity, especially for stand-alone systems where a serial interface has been addedwith no major design changes to the existing system. Essentially the additional port istreated like a keypad by the stand-alone device.Depending on the particular application, some of the tasks stand-alone devices arerequired to perform are as follows:• Take measurements from sensors at time intervals determined by the user• Make the measurements from sensors conditional on certain events orenvironments• Adjust the sensor measurement rate so that readings are taken more frequentlyduring conditions of greater interest• Mathematically combine and manipulate sensor readings• Apply statistical procedures to reduce the number of readings that need to bestored