A device including a PLD with at least one interface logic block connection for passing data between (i) a bus arranged for receiving data from an external processor and (ii) at least one I/O register connected with a JTAG interface of the PLD, wherein said interface logic block includes logic for translating data on the bus into a data format for the I/O register. A processor programmable PLD appliance comprising (a) a programmable PLD having a JTAG programming interface supporting real-time re-programming of the PLD while the PLD functions as programmed; and (b) an I/O register interfacing an I/O register and connected with the JTAG programming interface, wherein a PLD logic design implementation of the I/O register is externally accessible through an interface logic block of the PLD, and wherein the interface logic block includes a PLD path between (i) an external processor interface and (ii) the PLD-implemented I/O register.