The output interface module connects to: sensing devices such as switches or pushbuttons. load devices such as lamps or solenoids. a programming device such as a computer. all of the above. The power required to operate the logic circuits of the processor unit is typically: low voltage ac. low voltage dc. high voltage ac. high voltage dc. At the start of the PLC scan the: status of all inputs are read. status of all outputs are updated. program is executed. diagnostics and communications tasks are executed. A human machine interface (HMI) allows the user to monitor a process. allows the user to control a process. can provide a graphical representation of a process. all of the above. Programmable logic controllers are categorized according to the number of I/O points. current rating of I/O modules. power rating of the I/O modules