A programmable interface circuit including at least one channel for coupling a field device to a process controller block, said channel comprising: a digital logic block having a plurality of terminals including terminals configured for receiving control signals from said process controller block, terminals (111, 112) for providing a plurality of logic signals (111a, 112a); and at least a first processed data terminal for receiving processed signal data; an analog logic block coupled to receive a first portion of said logic signals including a current output digital to analog converter which provides a variable current source, and an output circuit block that includes first and second field terminals (S1 and S2) for connecting said field device across, and a sense resistor, wherein said variable current source is coupled to said S1 and said sense resistor is coupled to said S2; wherein said analog logic block further comprises a first and a second multi-channel multiplexer (131, 132) coupled to receive a second portion of said logic signals, an operational amplifier (op amp), and analog to digital converter, wherein said first and said second MUX are across said sense resistor and have their respective outputs coupled to respective inputs of said op amp, and wherein an output of said op amp is coupled to an input of said ADC, and an output of said ADC is coupled to provide said processed signal data to said processed data terminal of said digital logic block, wherein said control signals automatically select from a plurality of available signal modes for said programmable interface circuit including an analog output mode, a digital output mode, an analog input mode, a digital input mode, and at least one additional signal mode provided by adding a sub-mode to said AI mode or said DI mode. a digital logic block having a plurality of terminals including terminals configured for receiving control signals from said process controller block, terminals (111, 112) for providing a plurality of logic signals (111a, 112a); and at least a first processed data terminal for receiving processed signal data; an analog logic block coupled to receive a first portion of said logic signals including a current output digital to analog converter which provides a variable current source, and an output circuit block that includes first and second field terminals (S1 and S2) for connecting said field device across, and a sense resistor, wherein said variable current source is coupled to said S1 and said sense resistor is coupled to said S2; wherein said analog logic block further comprises a first and a second multi-channel multiplexer (131, 132) coupled to receive a second portion of said logic signals, an operational amplifier (op amp), and analog to digital converter, wherein said first and said second MUX are across said sense resistor and have their respective outputs coupled to respective inputs of said op amp, and wherein an output of said op amp is coupled to an input of said ADC, and an output of said ADC is coupled to provide said processed signal data to said processed data terminal of said digital logic block, wherein said control signals automatically select from a plurality of available signal modes for said programmable interface circuit including an analog output mode, a digital output mode, an analog input mode, a digital input mode, and at least one additional signal mode provided by adding a sub-mode to said AI mode or said DI mode.