Part A
74HC238D
東芝セミコンダクター・アンド・ストレージ
- Lifecycle
- Active
- Stock
- 5394 個数
- Package
- SOIC-16
- Series
- ロジック - 信号スイッチ、マルチプレクサ、デコーダ
Replacement verdict
Not a drop-in replacement
The 74HC245D and 74HC238D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-16 package. The 74HC245D is an octal bidirectional bus transceiver with three-state outputs, while the 74HC238D is a 3-to-8 line decoder/demultiplexer with active-low outputs. Their internal logic functions, pin assignments, and signal flow directions are fundamentally different, making direct substitution impossible without complete circuit redesign.
Different logic function
Different pin assignment
Different output type
Different signal 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 | 74HC245D | 74HC238D | Why it matters |
|---|---|---|---|
| Logic Function | Octal bus transceiver with 3-state outputs | 3-to-8 line decoder/demultiplexer | Defines the core function; these devices are not functionally interchangeable as they perform entirely different logic operations. |
| Number of Channels / Outputs | 8 bidirectional channels | 8 decoded outputs (from 3 inputs) | Determines how many signals can be routed or controlled, affecting system architecture and pin count requirements. |
| Direction Control | Yes (DIR pin selects A-to-B or B-to-A) | No (unidirectional decoding only) | Bidirectional capability is essential for bus interfacing, while a decoder is inherently unidirectional. |
| Output Type | 3-state (tri-state) outputs | Active-low outputs (non-tri-state) | Tri-state outputs allow bus sharing; standard active-low outputs do not, impacting multi-device bus configurations. |
| Enable / Control Inputs | OE (output enable) and DIR | Three enable inputs (G1, G2A, G2B) | Control inputs determine how the device is gated or selected within a larger digital system. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC-family voltage range, allowing use in 3.3 V and 5 V logic systems. |
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) | Identical package footprint means PCB layout compatibility, though pin functions differ. |
| Pin Count | 16 | 16 | Same pin count simplifies mechanical compatibility but does not imply electrical interchangeability. |
| Logic Family | HC (High-speed CMOS) | HC (High-speed CMOS) | Same logic family ensures compatible voltage thresholds and drive characteristics when interfacing with other HC devices. |
| Propagation Delay (typical at 5 V) | ~8 ns | ~14 ns | Timing differences affect maximum operating frequency and signal integrity in high-speed designs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC238D | 74HC245D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Transceiver, Non-Inverting |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Output Type | - | 3-State |
Frequently asked questions
What are the primary functions of the 74HC245D and 74HC238D?
The 74HC245D is an octal non-inverting bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74HC238D is a 3-to-8 line decoder/demultiplexer that accepts a 3-bit binary address and activates one of eight mutually exclusive outputs.
Can the 74HC245D and 74HC238D be used interchangeably in a circuit design?
No. They perform fundamentally different logic functions. The 74HC245D provides bidirectional signal buffering and bus isolation, while the 74HC238D performs address decoding and demultiplexing. Substitution would require a complete redesign of the surrounding circuitry.
What are the key differences in pin count and package type between the 74HC245D and 74HC238D?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in Nexperia and similar manufacturer nomenclature indicates SO16). However, their pinouts differ entirely due to their distinct logic functions. The 74HC245D includes direction control (DIR) and output enable (OE) pins, while the 74HC238D includes three address inputs (A0-A2), three enable inputs (E1, E2, E3), and eight decoded outputs (Y0-Y7).
What are the supply voltage and logic level specifications for the 74HC245D and 74HC238D?
Both devices are members of the 74HC high-speed CMOS family and operate over a recommended supply voltage range of 2.0 V to 6.0 V. They provide CMOS-level inputs and outputs compatible with standard 5 V TTL logic thresholds when operated at 5 V, per JEDEC standard 7A requirements.
How do the output drive capabilities of the 74HC245D and 74HC238D compare?
Both devices typically provide symmetrical CMOS output drive. At a 5 V supply, standard 74HC outputs are specified to source or sink at least 4 mA, with many manufacturers rating them up to 6 mA or higher. The 74HC245D's 3-state outputs and the 74HC238D's decoded outputs share similar drive strength characteristics within the same logic family.
What is the role of the direction (DIR) and output enable (OE) pins on the 74HC245D?
The DIR pin selects the data transmission direction: when DIR is HIGH, data flows from the A bus to the B bus; when DIR is LOW, data flows from the B bus to the A bus. The OE pin, when HIGH, places both A and B ports in a high-impedance state, effectively disconnecting the device from the buses.
How does the 74HC238D select which output is active?
The 74HC238D uses three address inputs (A0, A1, A2) to select one of eight outputs (Y0-Y7). The selected output goes HIGH while all others remain LOW, provided the enable inputs (E1 and E2 are active LOW, E3 is active HIGH) are in their active states. If any enable input is inactive, all outputs are forced LOW.
Are the 74HC245D and 74HC238D available in automotive-qualified versions?
Automotive-qualified variants exist for both functions under different part numbers (e.g., 74HCT245-Q100 and 74HCT238-Q100 from Nexperia). The standard 74HC245D and 74HC238D are commercial-grade devices. Designers requiring AEC-Q100 qualification must select the appropriately suffixed automotive part numbers.