Part A
74HC594D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 1976 PCS
- Package
- SOIC-16
- Series
- Logic - Shift Registers
Replacement verdict
Compatible functional replacement candidate
The 74HC595D and 74HC594D are both 8-bit serial-in/parallel-out shift registers with output latches in the same SOIC-16 package, sharing identical supply voltage, logic family, and pin count. However, the 74HC595D provides a serial data output for cascading and a direct asynchronous reset, while the 74HC594D offers a separate storage register clock and a shift register clear. These differences in output configuration and control architecture mean the 74HC595D is not a pin-for-pin drop-in replacement for the 74HC594D, and circuit-level validation is required before substitution.
Package Type
High match
Logic Function
High match
Output Configuration
Validation required
Control Interface
Not compatible
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC595D | 74HC594D | Why it matters |
|---|---|---|---|
| Function | 8-bit serial-in, serial/parallel-out shift register with output latches | 8-bit serial-in, serial/parallel-out shift register with output latches | Both are 8-bit shift registers with latches, but the 74HC595 has a separate serial output (Q7') for cascading, while the 74HC594 does not. |
| Serial Output (Q7') | Yes, provides serial data output for cascading | No serial output; only parallel outputs | The serial output allows multiple devices to be daisy-chained without additional I/O pins, which is critical for expanding output count. |
| Output Enable (OE) | Active-low output enable (OE) pin | No output enable pin; outputs always active | The OE pin on the 74HC595 allows the outputs to be tri-stated for bus sharing or dimming via PWM, which the 74HC594 cannot do. |
| Shift Register Clear | Asynchronous clear (SRCLR) resets shift register only | Asynchronous clear (SRCLR) resets shift register only | Both have a shift register clear, but the 74HC595 also has a separate latch clock, allowing independent control of shift and storage registers. |
| Latch Clock (RCLK) | Yes, separate latch clock (RCLK) for storage register | Yes, separate latch clock (RCLK) for storage register | The separate latch clock allows data to be shifted in without affecting outputs until the latch is clocked, enabling glitch-free updates. |
| Package | SO16 (D package) | SO16 (D package) | Both are in the same SO16 package, so they are footprint-compatible for PCB layout. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both operate over the standard HC family voltage range, making them suitable for 3.3 V and 5 V logic systems. |
| Output Current per Pin | ±6 mA (at 4.5 V) | ±6 mA (at 4.5 V) | Both can drive standard logic loads and small LEDs directly, but external drivers are needed for higher currents. |
| Propagation Delay (tpd) | Typical 15 ns at 4.5 V | Typical 15 ns at 4.5 V | Similar propagation delay means both can operate at comparable clock frequencies in typical applications. |
| Pin Count | 16 pins | 16 pins | Same pin count, but pin functions differ (e.g., OE and Q7' on 595 vs. no OE and no Q7' on 594), so they are not pin-to-pin compatible. |
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Send your BOM and application constraints for technical and sourcing review.
Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC594D | 74HC595D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Shift Register | Shift Register |
| Output Type | Push-Pull | Tri-State |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Function | Serial to Parallel, Serial | Serial to Parallel, Serial |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What is the primary functional difference between the 74HC595D and the 74HC594D?
The 74HC595D is an 8-bit serial-in, parallel-out shift register with a separate storage register and 3-state output buffers. The 74HC594D is an 8-bit serial-in, parallel-out shift register with a separate storage register but without 3-state output buffers; its parallel outputs are always active.
Are the 74HC595D and 74HC594D pin-compatible?
No. The 74HC595D includes an output enable (OE) pin that places the parallel outputs in high-impedance state, while the 74HC594D does not have an OE pin. The pinout differs accordingly, so they are not drop-in replacements.
Can the 74HC595D and 74HC594D be used in the same serial cascade configuration?
Yes. Both devices provide a serial data output (Q7') for cascading multiple shift registers. The serial input and shift clock timing are compatible, allowing either device to be chained with identical or matching types.
Which device should be selected when the parallel outputs must be disabled or tri-stated?
The 74HC595D must be selected because it has a dedicated output enable (OE) pin that forces the parallel outputs into high-impedance state. The 74HC594D lacks this function and cannot tri-state its parallel outputs.
Do both devices have the same supply voltage and logic level specifications?
Yes. Both the 74HC595D and 74HC594D are HC-family CMOS devices typically specified for 2.0 V to 6.0 V operation, with standard CMOS input thresholds and output drive characteristics as defined in their respective manufacturer datasheets.
What is the function of the storage register latch clock in both devices?
In both the 74HC595D and 74HC594D, the storage register latch clock (often labeled LATCH or RCLK) transfers data from the internal shift register to the parallel output register. This allows the outputs to update simultaneously while new serial data is shifted in.
Are the 74HC595D and 74HC594D available in the same package types?
Both devices are commonly offered in SOIC, TSSOP, and DIP packages by various manufacturers. However, exact package availability depends on the specific manufacturer and ordering part number, so the datasheet for the chosen device must be consulted.