Modifier function blocks in a process control system

摘要

Modification function block (54) can be called up conditionally according to state of base function block (52) to alter operation of base function block or to leave unchanged functionality of base function block. Each function block has software routine to control assigned processor. Base function block (52) has first row of processor implementable commands (55) allowing first processor to carry out function which is assigned to the process control routine. Modification function block (54) has second row of processor implementable commands (58) and is stored accessible by first processor. Resettable branch (56,57) has pointer, set to first value to allow first processor to carry out further processor implementable command (55) in base function block. Branch is set onto a second value for first processor to carry out second row of commands (58) in modification function block.