Part A
74HC245D,653
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Replacement verdict
Not a drop-in replacement
The 74HC238D and 74HC245D,653 are not functionally interchangeable. The 74HC238D is a 3-to-8 line decoder/demultiplexer with active-low outputs, while the 74HC245D,653 is an octal bidirectional bus transceiver with 3-state outputs. Their logic functions, pin configurations, and I/O structures are fundamentally different, making direct substitution impossible without circuit redesign.
Different logic function
Different output type
Different pinout
Different I/O direction
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC238D | 74HC245D,653 | Why it matters |
|---|---|---|---|
| Logic Function | 3-to-8 Line Decoder/Demultiplexer | Octal Bus Transceiver (3-State) | The core function determines whether the device can be substituted at all; a decoder and a bus transceiver perform fundamentally different logic operations. |
| Number of Outputs | 8 | 8 | Both provide eight outputs, but the output type and control differ, affecting how they interface with downstream circuitry. |
| Output Type | Active LOW (non-inverting, one-hot) | 3-State, non-inverting, bidirectional | Output polarity and drive type must match the target circuit; active-LOW decoded outputs versus 3-state bidirectional buffers are not interchangeable. |
| Direction Control | Unidirectional (decoder outputs) | Bidirectional via DIR pin | Bidirectional capability allows data flow in either direction, which a decoder cannot provide, limiting substitutability. |
| Enable / Control Inputs | 3 enable inputs (two active LOW, one active HIGH) | OE (Output Enable, active LOW) and DIR | Control pin configuration affects how the device is gated and cascaded in a system; different control schemes require different wiring. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Matching supply ranges ensures both devices operate in the same logic-level environment without level shifting. |
| Logic Family | HC (High-speed CMOS) | HC (High-speed CMOS) | Same logic family means compatible input thresholds, noise margins, and drive characteristics. |
| Propagation Delay (typical) | ~14 ns at 4.5 V | ~8 ns at 4.5 V | Timing differences can affect setup/hold margins and maximum operating frequency in synchronous designs. |
| Output Drive Current | ±4 mA (standard HC) | ±6 mA (standard HC) | Drive strength determines fan-out and ability to drive LEDs, buses, or other loads directly. |
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) | Same package footprint allows drop-in PCB compatibility, though pin functions differ. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC245D,653 | 74HC238D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Discontinued at DigiKey | Active |
| Base Product Number | 74HC245 | - |
| Logic Type | Transceiver, Non-Inverting | - |
| Number of Elements | 1 | - |
| Number of Bits per Element | 8 | - |
| Output Type | 3-State | - |
| Current - Output High, Low | 7.8mA, 7.8mA | - |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C (TA) | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Packaging | Tape & Reel (TR) | - |
| Type | - | Decoder/Demultiplexer |
| Circuit | - | 1 x 3:8 |
| 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 74HC238D and the 74HC245D,653?
The 74HC238D is a 3-to-8 line decoder/demultiplexer that takes a 3-bit binary address and activates one of eight mutually exclusive outputs. The 74HC245D,653 is an octal bus transceiver with 3-state outputs designed for bidirectional asynchronous communication between two data buses.
Can the 74HC238D and 74HC245D,653 be used interchangeably in a circuit design?
No. They perform fundamentally different logic functions. The 74HC238D decodes a binary input to select one of eight outputs, while the 74HC245D,653 provides bidirectional voltage-level translation and bus driving for eight data lines. Substitution requires a complete redesign of the surrounding circuitry.
What are the package and pin count differences between the 74HC238D and the 74HC245D,653?
The 74HC238D is typically supplied in a 16-pin SOIC package. The 74HC245D,653 is supplied in a 20-pin SOIC package. The different pin counts and pinouts prevent direct PCB footprint compatibility.
Do both devices operate at the same supply voltage range and logic family?
Yes. Both are members of the 74HC high-speed CMOS logic family and operate over a standard supply voltage range of 2.0 V to 6.0 V, with typical operation at 5.0 V. They are compatible with CMOS and TTL logic levels when used within the specified operating conditions.
What is the difference in output drive capability between the 74HC238D and the 74HC245D,653?
The 74HC238D provides standard CMOS output drive, typically ±4 mA at 5 V. The 74HC245D,653 is designed as a bus transceiver and provides higher output drive, typically ±6 mA at 5 V, making it more suitable for driving heavily loaded bus lines.
Does the 74HC245D,653 have a direction control pin that the 74HC238D lacks?
Yes. The 74HC245D,653 includes a direction control (DIR) pin that determines whether data flows from the A bus to the B bus or from the B bus to the A bus. The 74HC238D does not have a direction control pin because it is a unidirectional decoder/demultiplexer.
Are both devices available in automotive-qualified versions?
Automotive qualification depends on the specific manufacturer part number and suffix. The base 74HC238D and 74HC245D,653 are standard commercial/industrial grade devices. Automotive-qualified variants, where offered, are identified by separate manufacturer part numbers and should be verified against the specific manufacturer datasheet.
What are the typical propagation delay characteristics of the 74HC238D and the 74HC245D,653?
At a 5 V supply, the 74HC238D typically exhibits a propagation delay of approximately 12 ns from address input to output. The 74HC245D,653 typically exhibits a propagation delay of approximately 8 ns from A to B or B to A. Actual values vary with load capacitance and supply voltage per the manufacturer datasheet.