A microprocessor integrated circuit design has improved partitioning between integrated injection logic (I.sup.2 L) and transistor-transistor logic (T.sup.2 L) in the integrated circuit. An information bus structure incorporating a bidirectional input and output buffer and a bidirectional input and output multiplexer minimizes the number of internal bus lines in the integrated circuit. An improved T.sup.2 - I.sup.2 L interface circuit and structure supplies a T.sup.2 L input to a plurality of I.sup.2 L input stages, each having a restricted cross-sectional area resistor element in the base of an I.sup.2 L input transistor. A storage register in the integrated circuit has a multiplexer portion provided at each flip-flop circuit of the register. A high speed feed forward flip-flop circuit is employed in registers of the integrated circuit where speed is critical. An improved voltage regulator and current source combination in a programmable logic array (PLA) reduces PLA temperature sensitivity. A pair of I.sup.2 L clocking pulse input transistors in a T.sup.2 L master-slave circuit avoids capacitive coupling problems and allows the master-slave circuit to operate over a much wider temperature range. A cycle counter for the micro-processor integrated circuit implemented as an improved ripple down counter requires a minimum number of gates while avoiding significant delay in operation.