Dual microprocessor intelligent programmable process control system

An intelligent programmable process control system for controlling a process, said system comprising:

• (a) at least one analog-to-digital converter means for generating a digital output corresponding to an analog voltage input signal from an analog sensor device located along said process;
• (b) at least one digital-to-analog converter means for generating an analog voltage output signal corresponding to a digital input to control a controllable analog device located along said process;
• (c) first microprocessor means coupled to the digital output of said analog-to-digital converter means and coupled to provide the digital input to said digital-to-analog converter means, said first microprocessor means controlling at least one analog loop control function of said process via said analog-to-digital converter means and said digital-to-analog converter means;
• second microprocessor means for scanning and executing a sequence of boolean logic functions, said first microprocessor means and said second microprocessor means normally operating asynchronously with respect to each other;
• (d) image register means for storing input bits representative of the on/off states of sensors located along said process and output bits representative of the on/off states of controllable devices located along said process, said second microprocessor means being coupled to said image register means for executing said sequence of boolean logic functions in accordance with the states of said input bits to generate said output bits;
• (e) a random access memory;
• (f) address and data bus means providing a first coupling between said first and second microprocessor means through said random access memory, said first and second microprocessor means communicating with each other via selectively addressed memory locations of said random access memory, said address and data bus means further coupling said analog-to-digital converter means and said digital-to-analog converter means to said first microprocessor means, each of said analog-to-digital converter means and said digital-to-analog converter means being addressable by said first microprocessor means as extended memory locations of said random access memory;
• and
• (g) other means directly coupling said second microprocessor means to said first microprocessor means whereby said second microprocessor means signals said first microprocesssor means to perform digital operations and arithmetic computations for said second microprocessor means in addition to controlling said analog loop control functions.