Part A
74HC238D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 5394 PCS
- Package
- SOIC-16
- Series
- Lógica - Conmutadores de sinais, Multiplexers, Decodificadores
Replacement verdict
Not a drop-in replacement
The 74HC238D and 74HC245D,652 are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC238D is a 3-to-8 line decoder/demultiplexer with eight mutually exclusive active-low outputs, while the 74HC245D,652 is an octal bidirectional transceiver with dual-direction bus control. Their internal architectures, pin functions, and control logic differ fundamentally, so neither device can directly replace the other in an existing design without significant circuit redesign.
Different logic function
Different output type
Different channel count
Different control interface
Parts at a glance
Part B
74HC245D,652
NXP USA Inc.
- Lifecycle
- Active
- Stock
- 4100 PCS
- Package
- SOIC-20
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
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,652 | Why it matters |
|---|---|---|---|
| Logic Function | 3-to-8 line decoder/demultiplexer | Octal bus transceiver with 3-state outputs | The core function determines whether the device can be substituted at all; a decoder and a bus transceiver serve fundamentally different roles in a circuit. |
| Number of Channels / Outputs | 8 outputs (one of eight decoded) | 8 bidirectional channels | Channel count and directionality affect how many signals can be routed and whether data can flow both ways. |
| Directionality | Unidirectional (inputs to decoded outputs) | Bidirectional (A-to-B or B-to-A controlled by DIR) | Bidirectional capability is essential for bus interfacing, while a decoder is strictly unidirectional. |
| Output Type | Active-low decoded outputs (non-3-state) | 3-state outputs | 3-state outputs allow bus sharing by high-impedance disconnection, which the decoder cannot provide. |
| Control Inputs | 3 address inputs plus 3 enable inputs (two active-low, one active-high) | Direction (DIR) and Output Enable (OE) inputs | Control pin configuration determines how the device is driven and whether it fits the intended logic scheme. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Matching supply voltage ranges ensures compatibility with the target system's power rail. |
| Logic Family | HC (High-speed CMOS) | HC (High-speed CMOS) | Same logic family implies compatible input thresholds, noise margins, and drive characteristics. |
| Package | SO16 (SOIC-16) | SO20 (SOIC-20) | Different package footprints and pin counts prevent direct drop-in replacement on the same PCB pad layout. |
| Pin Count | 16 pins | 20 pins | Pin count mismatch means the devices are not pin-compatible and cannot share the same socket. |
| Typical Propagation Delay | Approximately 14 ns at 4.5 V | Approximately 8 ns at 4.5 V | Propagation delay affects timing margins in high-speed digital systems and can impact signal integrity. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC238D | 74HC245D,652 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | - | Transceiver, Non-Inverting |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Output Type | - | 3-State |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Voltage Supply Source | Single Supply | - |
Frequently asked questions
What are the primary functions of the 74HC238D and the 74HC245D,652?
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. The 74HC245D,652 is an octal bus transceiver with 3-state outputs designed for bidirectional asynchronous communication between two data buses.
Can the 74HC238D and 74HC245D,652 be used interchangeably in a design?
No. They perform fundamentally different logic functions. The 74HC238D decodes a binary input into one active output, while the 74HC245D,652 provides bidirectional voltage-level translation and bus driving for eight data lines. Substitution requires a complete redesign of the surrounding circuit.
What are the key differences in pin count and package type between the two devices?
The 74HC238D is typically supplied in a 16-pin SOIC package. The 74HC245D,652 is typically supplied in a 20-pin SOIC package. Pin counts and pinouts differ, so PCB land patterns are not compatible.
Do both devices operate from the same supply voltage range?
Yes. Both the 74HC238D and the 74HC245D,652 are HC-family CMOS devices specified for a supply voltage range of 2.0 V to 6.0 V, with typical operation at 5.0 V.
How do the output drive capabilities of the 74HC238D and 74HC245D,652 compare?
Both devices provide standard HC-family output drive. The 74HC238D has active-low outputs capable of driving standard CMOS or TTL loads. The 74HC245D,652 has 3-state outputs with similar drive strength per channel, but it is optimized for bus driving with both source and sink capability.
What is the role of the direction control (DIR) pin on the 74HC245D,652 compared to the enable inputs on the 74HC238D?
The 74HC245D,652 uses a DIR pin to select data flow from A to B or B to A, and an OE pin to enable or disable the outputs. The 74HC238D uses three enable inputs (two active-low, one active-high) to gate the decoder outputs, but it does not support bidirectional data flow.
Are the 74HC238D and 74HC245D,652 both available in the same SOIC package footprint?
No. The 74HC238D is a 16-pin SOIC (D package), while the 74HC245D,652 is a 20-pin SOIC (D package). The package widths may be similar, but the pin counts and pin assignments differ, preventing footprint compatibility.
Which device is better suited for expanding microcontroller I/O, and which for bus isolation?
The 74HC238D is suited for address decoding or I/O expansion where one of eight outputs must be selected. The 74HC245D,652 is suited for bus isolation, level shifting, or bidirectional data transfer between two buses.