6 Detailed Description

6.1 Overview

The RCA CD54/74AC299 and CD54/74AC323 and the CD54/74ACT299 and CD54/74ACT323 are 3-state,

8-input universal shift/storage registers with common parallel I/O pins. These devices use the RCA ADVANCED

CMOS technology. These registers have 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 (DSO, DS7), and the Parallel

Data (l/O0 - l/O7) respond only to the LOW-TO-HIGH transition of the clock (CP) pulse. S0, S1 and Data inputs

must be present one setup time prior to the positive transition of the clock.

With the CD54/74AC/ACT299, the Master Reset (MR) is an asynchronous active-LOW input. When MR is LOW,

the register is cleared regardless of the status of all other inputs With the CD54/74AC/ACT323, the Master Reset

(MR) clears the register in sync with the clock input. The register can be expanded by cascading same units by

tying the serial output (QO) to the serial data (DS7) input of the preceding register, and tying the serial output

(Q7) to the serial data (DSO) input of the following register. Recirculating the (n x 8) bits is accomplished by tying

the Q7 of the last stage to the DSO of the first stage.

The 3-state input/output (I/O) port has three modes of operation:

1. Both Output Enable (ΟΕ1 and OE2) inputs are LOW and S0 or S1 or both are LOW; the data in the register

is present at the eight outputs.

2. When both S0 and S1 are HIGH, I/O terminals are in the high-impedance state but being input ports, ready

for parallel data to be loaded into eight registers with one clock transition regardless of the status of OE1 and

OE2.

3. Either one of the two Output Enable inputs being HIGH will force I/O terminals to be in the off state. It is

noted that each I/O terminal is a 3-state output and a CMOS buffer input.

The CD74AC/ACT299 and CD74AC/ACT323 are supplied in 20-lead dual-in-line plastic packages (E suffix)

and in 20-lead dual-in-line small-outline plastic packages (M suffix). Both package types are operable over

the following temperature ranges: Commercial (0 to 70°C); Industrial (-40 to +85° C); and Extended Industrial/

Military (-55 to +125° C).

The CD54AC/ACT299 and CD54AC/ACT323, available in chip form (H suffix), are operable over the -55 to

+125°C temperature range.

6.2 Functional Block Diagram

Figure 6-1. Functional Diagram

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CD54AC299, CD74AC299, CD74AC323, CD54ACT299, CD74ACT299

SCHS288A – DECEMBER 1998 – REVISED DECEMBER 2024

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