In a factory setting, it's rare that a machine is dedicated to one style part for its application. For example, Machine A does a dispense pattern of sealant on small outboard motor engine blocks. The dispense pattern differs depending on which engine block is being run. The SEL Programming Language accommodates for cases where multiple parts are being run on a single machine. By using the I/O or serial communication, the user can send over a signal telling the SEL controller which section of code to perform. After the code is run, the inputs (or serial strings) are checked again to determine which route to take.
In the example above, inputs 5, 6, 7 and 8 are being checked for active conditions. Since a separate subroutine is being executed based on which input is active, only one input is checked at any given time. In other words, the polling of inputs is done sequentially, not all at the same time.