Part A
74HC594D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 1976 PCS
- Package
- SOIC-16
- Series
- Logique - Registre à décalage
Replacement verdict
Not a drop-in replacement
The 74HC574D and 74HC594D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-16 package. The 74HC574D is an octal D-type flip-flop with 3-state outputs intended for parallel data storage and bus interfacing, while the 74HC594D is an 8-bit serial-in/parallel-out shift register with an integrated output register and serial output for cascading. Their internal architecture, pin functions, and control logic differ fundamentally, so direct substitution is not possible without redesigning the surrounding circuitry.
Different logic function
Different input interface
Different output configuration
Different control signals
Parts at a glance
Part B
74HC574D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 3287 PCS
- Package
- SOIC-20
- Series
- Logique - Triggers
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC574D | 74HC594D | Why it matters |
|---|---|---|---|
| Logic Function | Octal D-type flip-flop, positive edge triggered, 3-state outputs | 8-bit serial-in/parallel-out shift register with output register | The core function differs: the 574 latches parallel data on a clock edge, while the 594 shifts serial data in and latches it to parallel outputs, so they are not functionally interchangeable. |
| Data Input Type | Parallel (8-bit D inputs) | Serial (single DS input) | Input format determines how data is loaded; parallel loading versus serial shifting requires different driving circuitry and control signals. |
| Output Type | 3-state parallel outputs | Parallel outputs (non-3-state) plus serial output QH' | 3-state outputs allow bus sharing, whereas the 594's always-active outputs and serial output suit cascaded shift-register chains. |
| Number of Flip-Flops / Register Stages | 8 D-type flip-flops | 8-bit shift register plus 8-bit output register | The 594 contains two register stages (shift and storage), enabling simultaneous shifting and static output holding, which the 574 cannot do. |
| Control Inputs | Clock (CP) and Output Enable (OE) | Shift Clock (SHCP), Storage Clock (STCP), Output Enable (OE), Master Reset (MR) | Different control pin sets mean the devices require different timing and reset logic in a design. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC-family supply range, so power supply compatibility is identical. |
| Logic Family | 74HC (high-speed CMOS) | 74HC (high-speed CMOS) | Same logic family ensures comparable input/output thresholds, noise margins, and interfacing behavior. |
| Package | SO16 (D package) | SO16 (D package) | Identical package and pin count allow the same PCB footprint, though pin functions differ. |
| Pin Count | 20 pins | 16 pins | Different pin counts mean the devices are not drop-in compatible on the same footprint. |
| Maximum Clock Frequency | Typically up to 60 MHz at 4.5 V | Typically up to 60 MHz at 4.5 V (shift clock) | While nominal speed grades are similar, the 594's serial shifting limits effective throughput compared to the 574's parallel latching. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC594D | 74HC574D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Shift Register | - |
| Output Type | Push-Pull | Tri-State, Non-Inverted |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Function | Serial to Parallel, Serial | Standard |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Type | - | D-Type |
| Clock Frequency | - | 59 MHz |
| Max Propagation Delay @ V Max CL | - | 33ns @ 6V, 150pF |
| Trigger Type | - | Positive Edge |
| Current - Output High Low | - | 7.8mA, 7.8mA |
| Current - Quiescent (Iq) | - | 4 µA |
| Input Capacitance | - | 5 pF |
Frequently asked questions
What are the primary functional differences between the 74HC574D and the 74HC594D?
The 74HC574D is an octal D-type flip-flop with 3-state outputs, featuring a common clock and output enable. The 74HC594D is an 8-bit serial-in/parallel-out shift register with a storage register and 3-state outputs. The 574D is used for parallel data latching, while the 594D is used for serial-to-parallel data conversion.
Are the 74HC574D and 74HC594D pin-compatible?
No. The 74HC574D and 74HC594D have different pinouts. The 74HC574D has eight parallel data inputs (D0–D7), a clock (CP), an output enable (OE), and eight 3-state outputs (Q0–Q7). The 74HC594D has a serial data input (DS), a shift clock (SHCP), a storage clock (STCP), a reset (MR), a serial output (Q7S), and eight parallel outputs (Q0–Q7). They are not direct drop-in replacements.
Can the 74HC574D be used as a serial-to-parallel converter like the 74HC594D?
No. The 74HC574D is a parallel-in/parallel-out D-type flip-flop. It does not contain an internal shift register, so it cannot accept serial data and convert it to parallel output. The 74HC594D is specifically designed for serial-in/parallel-out operation.
Do both devices operate at the same supply voltage range and logic family levels?
Yes. Both the 74HC574D and 74HC594D are members of the 74HC CMOS logic family. They typically operate over a supply voltage range of 2.0 V to 6.0 V and provide standard CMOS input and output levels compatible with other 74HC devices.
What is the function of the output enable (OE) pin on each device?
On the 74HC574D, the OE pin controls the 3-state outputs: when OE is low, the outputs are active; when OE is high, the outputs are in high-impedance state. On the 74HC594D, the OE pin similarly controls the 3-state parallel outputs (Q0–Q7), while the serial output (Q7S) is not affected by OE.
Which device is better suited for expanding microcontroller I/O with minimal pin count?
The 74HC594D is generally better suited for expanding I/O with minimal pin count because it requires only three control lines (serial data, shift clock, storage clock) plus a reset to drive eight parallel outputs. The 74HC574D requires eight parallel data lines plus clock and output enable, consuming more microcontroller pins.
Can the 74HC594D be used to drive LEDs directly, and how does it compare to the 74HC574D for this purpose?
Both devices can drive LEDs, but their output current specifications must be respected. The 74HC594D provides eight parallel outputs with 3-state control, making it suitable for serial-to-parallel LED driving with fewer control pins. The 74HC574D provides eight parallel latched outputs, which is useful when parallel data is already available. In both cases, external current-limiting resistors or driver transistors may be required depending on LED current and supply voltage.
Are the 74HC574D and 74HC594D available in the same package type?
Both the 74HC574D and 74HC594D are commonly offered in SO14 (D) packages by various manufacturers. However, package availability can vary by manufacturer and specific ordering part number. Always verify the exact package suffix and mechanical dimensions from the manufacturer datasheet before designing a PCB footprint.