HEF4043BT Quad R/S Latch: Datasheet, Pinout, and Application Circuit Guide
The HEF4043BT is an integrated circuit from the ubiquitous 4000 series CMOS logic family. It contains four independent set/reset (R/S) latches, each with a complementary output. A key feature of this IC is its 3-state output capability, allowing the outputs to be put into a high-impedance state. This makes it exceptionally useful for bus-oriented systems and other applications where multiple devices must share a common line.
This guide provides a detailed overview of the HEF4043BT's pinout, functionality, and practical application circuits.
Datasheet Overview and Key Specifications
The HEF4043BT operates over a wide voltage range, typically from 3V to 15V, making it compatible with various logic levels and power supplies. Its CMOS technology ensures very low power consumption, especially in static conditions.
Key electrical characteristics include:
Supply Voltage Range (VDD): -0.5V to +18V
High-Level Output Current (IOH): -1.5mA @ VDD = 5V
Low-Level Output Current (IOL): 1.5mA @ VDD = 5V
Propagation Delay: Typically 150ns @ VDD = 5V, CL = 50pF
The device is also characterized by high noise immunity, a standard feature of CMOS ICs. For complete details, always refer to the official manufacturer's datasheet.
Pinout Configuration and Functionality
The HEF4043BT is housed in a 16-pin DIP (Dual In-line Package) or SOIC package. Its pinout is logically arranged for ease of use.
Pin Description:
Pin 1 (Q1): Output of Latch 1
Pin 2 (S1): Set Input for Latch 1 (Active HIGH)
Pin 3 (R1): Reset Input for Latch 1 (Active HIGH)
Pin 4 (Q2): Output of Latch 2
Pin 5 (S2): Set Input for Latch 2
Pin 6 (R2): Reset Input for Latch 2
Pin 7 (Enable 3,4): Enable Input for Latches 3 and 4 (Active HIGH)
Pin 8 (VSS): Ground (0V)
Pin 9 (S3): Set Input for Latch 3
Pin 10 (R3): Reset Input for Latch 3
Pin 11 (Q3): Output of Latch 3
Pin 12 (S4): Set Input for Latch 4
Pin 13 (R4): Reset Input for Latch 4
Pin 14 (Q4): Output of Latch 4
Pin 15 (Enable 1,2): Enable Input for Latches 1 and 2 (Active HIGH)
Pin 16 (VDD): Positive Supply Voltage
Truth Table (for a single latch):
| Enable | S (Set) | R (Reset) | Q (Output) | \Q (Not Output) |
| :----: | :-----: | :-------: | :--------: | :--------------: |
| L | X | X | High-Z (Off) | High-Z (Off) |
| H | H | L | H | L |
| H | L | H | L | H |
| H | L | L | Last Q | Last \Q |
| H | H | H | L | L |
Note: The invalid state (S=H, R=H) forces both true and complementary outputs LOW on the HEF4043BT, which is a specific characteristic of this "R/S Latch with 3-state" design.
Application Circuit Guide
1. Basic R/S Latch Debouncer:
A primary use for a single latch is switch debouncing. Mechanical switches generate multiple bounces when toggled, which a microcontroller might read as multiple presses. The R/S latch provides a clean, bounce-free output.
Circuit: Connect a push-button switch between VDD and the Set (S) pin. Connect a second switch between VDD and the Reset (R) pin. Both S and R pins require pull-down resistors to ground (e.g., 10kΩ). The output (Q) will go HIGH upon pressing the Set switch and remain HIGH until the Reset switch is pressed, completely ignoring any contact bouncing.
2. 4-Bit Data Latch with 3-State Bus Interface:
The 3-state output feature allows the HEF4043BT to be used as a 4-bit data latch connected to a shared data bus.
Circuit: The four data inputs are connected to the S pins of each latch (the R pins are held LOW or driven by inverted data). The four outputs (Q1-Q4) are tied together to form a 4-bit bus. The two Enable pins (for latches 1&2 and 3&4) can be controlled together or separately. When the Enable pin is HIGH, the latched data appears on the bus. When the Enable is LOW, those outputs enter a high-impedance state, effectively disconnecting from the bus so another device can drive it.
3. Simple Memory for Control Signals:
The latches can be used to store the state of control signals (e.g., alarm triggers, status indicators) even after the initiating event has passed. The signal is applied to the Set input, latching the output HIGH until a system reset is applied to the Reset input.
ICGOODFIND: The HEF4043BT remains a versatile and robust solution for basic digital memory tasks. Its primary advantages are its simple latching logic, wide voltage range, and critical 3-state output capability. It is perfectly suited for applications like switch debouncing, temporary data storage, and interfacing with microprocessor buses, offering a reliable and low-power alternative to discrete logic gates.
Keywords: R/S Latch, 3-State Output, Switch Debouncing, CMOS Logic, Data Storage
