74F433 Datasheet, PDF (3/16 Pages) Fairchild Semiconductor – First-In First-Out (FIFO) Buffer Memory

Functional Description
As shown in the block diagram, the 74F433 consists of
three sections:
1. An Input Register with parallel and serial data inputs,
as well as control inputs and outputs for input hand-
shaking and expansion.
2. A 4-bit-wide, 62-word-deep fall-through stack with self-
contained control logic.
3. An Output Register with parallel and serial data out-
puts, as well as control inputs and outputs for output
handshaking and expansion.
These three sections operate asynchronously and are vir-
tually independent of one another.
Input Register (Data Entry)
The Input Register can receive data in either bit-serial or 4-
bit parallel form. It stores this data until it is sent to the fall-
through stack, and also generates the necessary status
and control signals.
This 5-bit register (see Figure 1) is initialized by setting flip-
flop F₃ and resetting the other flip-flops. The Q-output of
the last flip-flop (FC) is brought out as the Input Register
Full (IRF) signal. After initialization, this output is HIGH.
Parallel Entry—A HIGH on the Parallel Load (PL) input
loads the D₀–D₃ inputs into the F₀–F₃ flip-flops and sets
the FC flip-flop. This forces the IRF output LOW, indicating
that the input register is full. During parallel entry, the Serial
Input Clock (CPSI) input must be LOW.
Serial Entry—Data on the Serial Data (D_S) input is serially
entered into the shift register (F₃, F₂, F₁, F₀, FC) on each
HIGH-to-LOW transition of the CPSI input when the Serial
Input Enable (IES) signal is LOW. During serial entry, the
PL input should be LOW.
After the fourth clock transition, the four data bits are
located in flip-flops F₀–F₃. The FC flip-flop is set, forcing
the IRF output LOW and internally inhibiting CPSI pulses
from affecting the register. Figure 2 illustrates the final posi-
tions in an 74F433 resulting from a 256-bit serial bit train
(B₀ is the first bit, B₂₅₅ the last).
FIGURE 1. Conceptual Input Section
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