74F194 4-bit bidirectional universal shift register
The functional characteristics of the 74F194 4-Bit Bidirectional Shift
Register are indicated in the Logic Diagram and Function Table. The
register is fully synchronous, with all operations taking place in less
than 9ns (typical) for 74F, making the device especially useful for
implementing very high speed CPUs, or for memory buffer registers.
The 74F194 design has special logic features which increase the
range of application. The synchronous operation of the device is
determined by two Mode Select inputs, S0 and S1. As shown in the
Mode Select-Function Table, data can be entered and shifted from
left to right (shift right, Q0"Q1, etc.), or right to left (shift left,
Q3"Q2, etc.), or parallel data can be entered, loading all 4 bits of
the register simultaneously. When both S0 and S1 are Low, existing
data is retained in a hold (do nothing) mode. The first and last
stages provide D-type Serial Data inputs (DSR, DSL) to allow
multistage shift right or shift left data transfers without interfering
with parallel load operation. Mode Select and data inputs on the
74F194 are edge-triggered, responding only to the Low-to-High
transition of the Clock (CP). Therefore, the only timing restriction is
that the Mode Select and selected data inputs must be stable one
setup time prior to the Low-to-High transition of the clock pulse.
Signals on the Mode Select, Parallel Data (D0–D3) and Serial Data
(DSR, DSL) can change when the clock is in either state, provided
only the recommended setup and hold times, with respect to the
clock rising edge, are observed. The four Parallel Data inputs
(D0–D3) are D-type inputs. Data appearing on (D0–D3) inputs when
S0 and S1 are High is transferred to the Q0–Q3 outputs
respectively, following the next Low-to-High transition of the clock.
When Low, the asynchronous Master Reset (MR) overrides all other
input conditions and forces the Q outputs Low.