Part A
74HC157D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 7197 PCS
- Package
- SOIC-16
- Series
- Logic - Signal Switches, Multiplexers, Decoders
Replacement verdict
Not a drop-in replacement
The 74HC157D and 74HC166D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-16 package. The 74HC157D is a quad 2-input multiplexer that selects between two data sources, while the 74HC166D is an 8-bit parallel-in/serial-out shift register. Their internal architectures, pin functions, and logic operations are fundamentally different, so neither device can directly substitute for the other in an existing design without significant circuit redesign.
Different logic function
Different pinout
Different data flow
Different control signals
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC157D | 74HC166D | Why it matters |
|---|---|---|---|
| Function | Quad 2-input multiplexer | 8-bit parallel-in/serial-out shift register | The core logic function differs, so these devices are not functionally interchangeable in a circuit. |
| Logic Type | Multiplexer | Shift Register | Different logic families perform different data routing and storage operations. |
| Number of Circuits | 4 | 1 | The number of independent channels affects how many signals can be processed simultaneously. |
| Number of Inputs per Circuit | 2 | 9 (8 parallel + serial) | Input count determines how many data sources can be selected or loaded. |
| Number of Outputs per Circuit | 1 | 1 (serial) | Output configuration affects how data is delivered to downstream stages. |
| Output Type | 3-State | 3-State | Both support bus sharing, but the output data format differs due to the underlying function. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Compatible supply voltages allow use in similar logic-level systems. |
| Propagation Delay | Typically 11 ns at 5 V | Typically 14 ns at 5 V | Timing differences can affect maximum operating frequency and signal integrity. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Similar temperature ratings indicate comparable environmental robustness. |
| Package | SOIC-16 | SOIC-16 | Matching package and pin count can simplify board layout, but pin functions differ. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC157D | 74HC166D |
|---|---|---|
| Supplier | - | Toshiba Semiconductor and Storage |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | - | Shift Register |
| Output Type | - | Push-Pull |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Function | - | Parallel or Serial to Serial |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Type | Multiplexer | - |
| Circuit | 4 x 2:1 | - |
| Independent Circuits | 1 | - |
| Current - Output High Low | 5.2mA, 5.2mA | - |
| Voltage Supply Source | Single Supply | - |
Frequently asked questions
What are the primary functions of the 74HC157D and 74HC166D?
The 74HC157D is a quad 2-input multiplexer that selects one of two 4-bit data sources based on a common select input. The 74HC166D is an 8-bit parallel-in/serial-out shift register with a synchronous parallel load and an asynchronous clear input.
Are the 74HC157D and 74HC166D pin-compatible?
No. The 74HC157D is typically supplied in a 16-pin SOIC package, while the 74HC166D is typically supplied in a 16-pin SOIC package as well, but their pin functions differ entirely. The 74HC157D has data inputs, select, and enable pins, whereas the 74HC166D has parallel load, clock, clear, and serial data pins. They cannot be interchanged without redesigning the circuit.
Can the 74HC157D and 74HC166D operate at the same supply voltage range?
Yes. Both devices are members of the 74HC family and typically operate over a supply voltage range of 2.0 V to 6.0 V, with characterized operation at 5.0 V. Always verify the specific manufacturer datasheet for exact limits.
What is the difference in logic function between the 74HC157D and 74HC166D?
The 74HC157D performs combinational logic multiplexing: it routes one of two 4-bit inputs to a 4-bit output. The 74HC166D performs sequential logic: it loads 8 bits in parallel and shifts them out serially on each clock pulse, with an asynchronous clear.
Which device is suitable for serial data transmission, the 74HC157D or the 74HC166D?
The 74HC166D is suitable for serial data transmission because it is an 8-bit parallel-in/serial-out shift register. The 74HC157D is a multiplexer and does not perform serialization.
Do both the 74HC157D and 74HC166D have Schmitt-trigger inputs?
No. Standard 74HC157D and 74HC166D devices do not have Schmitt-trigger inputs. They have standard CMOS input structures. Schmitt-trigger versions, if available, would be identified by a different part number suffix.
What are the typical propagation delays for the 74HC157D and 74HC166D?
At 5.0 V supply, the 74HC157D typically has a propagation delay from data input to output of approximately 12 ns to 20 ns, depending on the manufacturer. The 74HC166D typically has a clock-to-serial-output propagation delay of approximately 15 ns to 25 ns. Always consult the specific manufacturer datasheet for guaranteed limits.
Can the 74HC157D and 74HC166D be used in the same design without level shifting?
Yes, if both devices are powered from the same supply voltage within the 74HC family range (2.0 V to 6.0 V) and the logic levels are compatible. No level shifting is required between them when they share the same VCC.
Are the 74HC157D and 74HC166D available in identical package types?
Both are commonly available in 16-pin SOIC (D suffix) packages, as well as other packages such as TSSOP and PDIP. However, package availability varies by manufacturer. Always confirm the exact package code in the manufacturer datasheet or distributor listing.