Fieldbus control with embedded fieldbus 319Fieldbus control interfaceThe communication between a fieldbus system and the drive consists of 16-bit inputand output data words (with the ABB drives profile) and 32-bit input and output words(with the DCU profile). Control word and Status wordThe Control word (CW) is the principal means of controlling the drive from a fieldbussystem. The Control word is sent by the fieldbus controller to the drive. The driveswitches between its states according to the bit-coded instructions of the Controlword.The Status word (SW) is a word containing status information, sent by the drive to thefieldbus controller. ReferencesReferences (REF) are 16-bit signed integers. A negative reference (eg, reversedirection of rotation) is formed by calculating the two’s complement from thecorresponding positive reference value. The contents of each reference word can beused as the speed, frequency, torque or process reference. Actual valuesActual values (ACT) are 16-bit words containing selected values of the drive.
