The ’HC259 and ’HCT299 are 8-bit shift/storage registers with three-state bus interface capability. The register has four synchronous-operating modes controlled by the two select inputs as shown in the mode select (S0, S1) table. The mode select, the serial data (DS0, DS7) and the parallel data (I/O₀ – I/O₇) respond only to the low-to-high transition of the clock (CP) pulse. S0, S1 and data inputs must be one set-up time prior to the clock positive transition.

The Master Reset (MR)\ is an asynchronous active low input. When MR\ output is low, the register is cleared regardless of the status of all other inputs. The register can be expanded by cascading same units by tying the serial output (Q0) to the serial data (DS7) input of the preceding register, and tying the serial output (Q7) to the serial data (DS0) input of the following register.