Part A
74HC259D
Toshiba Semiconductor và lưu trữ
- Lifecycle
- Active
- Stock
- 7207 PCS
- Package
- SOIC-20
- Series
- Logic - Latches
Replacement verdict
Not a drop-in replacement
The 74HC259D and 74HC21D,653 are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC259D is an 8-bit addressable latch with 3-to-8 decoding and individual bit storage, while the 74HC21D,653 is a dual 4-input AND gate with no latching or addressing capability. Their internal architectures, pin functions, and logic operations differ fundamentally, making direct replacement impossible without complete circuit redesign.
Different logic function
Different output type
Different pin function
Different channel count
Parts at a glance
Part B
74HC21D,653
NXP bán dẫn
- Lifecycle
- Active
- Stock
- 8890 PCS
- Series
- Logic - Gates and Inverters
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC259D | 74HC21D,653 | Why it matters |
|---|---|---|---|
| Logic Function | 8-bit addressable latch | Dual 4-input AND gate | The core logic function determines whether the device can perform the intended signal processing role; these two parts are functionally unrelated and cannot substitute for each other. |
| Number of Gates / Latches | 8 latches (1-of-8 decoder/latch) | 2 gates | The count of internal logic elements defines how many independent signal paths the device can handle in a circuit. |
| Number of Inputs per Element | 1 data input plus 3 address inputs | 4 inputs per gate | Input count per element affects the logic complexity and the number of signals that must be routed to the device. |
| Number of Outputs | 8 outputs (Q0-Q7) | 2 outputs | Output count determines how many downstream loads or signal destinations the device can drive. |
| Output Type | Standard push-pull (with active-low reset) | Standard push-pull | Output type affects drive capability, interfacing compatibility, and whether external pull-up or pull-down resistors are needed. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | The supply voltage range must match the system rail to ensure reliable logic-level operation and avoid damage. |
| Propagation Delay | Typically 15 ns at 5 V | Typically 11 ns at 5 V | Propagation delay influences maximum operating frequency and timing margins in synchronous or cascaded logic designs. |
| Package / Mounting | SOIC-16, surface mount | SO-14, surface mount | Package footprint and pin count must match the PCB layout; a different package cannot be dropped into the same board location. |
| Pin Count | 16 pins | 14 pins | Pin count determines the physical and electrical interface; mismatched pin counts prevent direct substitution. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | The temperature range must cover the application environment to guarantee specified logic performance and reliability. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC259D | 74HC21D,653 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Part Status | Active | Active |
| Series | 74HC | - |
| Logic Type | D-Type, Addressable | - |
| Circuit | 1:8 | - |
| Output Type | Standard | - |
| Voltage - Supply | 2V ~ 6V | - |
| Independent Circuits | 1 | - |
| Delay Time - Propagation | 22ns | - |
| Current - Output High Low | 5.2mA, 5.2mA | - |
| Operating Temperature | -40°C ~ 125°C | - |
| Mounting Type | Surface Mount | - |
Frequently asked questions
What are the primary functional differences between the 74HC259D and the 74HC21D,653?
The 74HC259D is an 8-bit addressable latch, while the 74HC21D,653 is a dual 4-input AND gate. They perform entirely different logic functions and are not functionally interchangeable.
Can the 74HC259D and 74HC21D,653 be used as direct substitutes for each other?
No. The 74HC259D is an addressable latch with 8 outputs, and the 74HC21D,653 is a dual 4-input AND gate. Their pin functions, logic operations, and internal architectures are fundamentally different, so direct substitution is not possible.
Do the 74HC259D and 74HC21D,653 share the same package and pinout?
Both devices are typically offered in SO16 (SOIC-16) packages, but their pinouts differ. The 74HC259D uses pins for address inputs, data input, latch enable, and eight outputs, while the 74HC21D,653 uses pins for two independent 4-input AND gates, VCC, and GND. Pin-to-pin compatibility is therefore not present.
What are the typical operating voltage and logic family specifications for these devices?
Both the 74HC259D and 74HC21D,653 belong to the 74HC high-speed CMOS logic family. They typically operate over a supply voltage range of 2.0 V to 6.0 V, with standard 74HC input and output characteristics as specified in their respective manufacturer datasheets.
Which device is better suited for latching or storing data bits?
The 74HC259D is the appropriate choice for latching or storing data bits because it is an 8-bit addressable latch. The 74HC21D,653 is a combinational logic gate and does not provide any latching or storage function.
Which device is intended for implementing combinational logic such as AND operations?
The 74HC21D,653 is intended for combinational logic, specifically providing two independent 4-input AND gates. The 74HC259D does not implement AND gate logic and cannot replace the 74HC21D,653 in such applications.
Are the 74HC259D and 74HC21D,653 interchangeable in existing PCB designs?
No. Because their pin functions and internal logic differ, replacing one with the other in an existing PCB design would require significant redesign of the circuit and layout. They are not drop-in replacements.