Part A
74HCT245D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 6073 ПКС
- Package
- SOIC-14
- Series
- Логика - буферы, драйверы, приемники, передатчики
Replacement verdict
Not a drop-in replacement
The 74HCT245D and 74HCT373D,653 are not functionally interchangeable despite sharing the same 74HCT logic family and SO-16 package. The 74HCT245D is an octal bus transceiver with dual-direction data flow and 3-state outputs, while the 74HCT373D,653 is an octal D-type transparent latch with single-direction data flow and 3-state outputs. Their internal logic functions, pinout signal assignments, and control architectures differ fundamentally, so direct substitution in an existing design is not possible without circuit redesign.
Different logic function
Different data direction
Different control architecture
Different pinout assignment
Parts at a glance
Part B
74HCT373D,653
Компания NXP USA Inc.
- Lifecycle
- Active
- Stock
- 8194 ПКС
- Package
- SOIC-20
- Series
- Логика - Заключения
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT245D | 74HCT373D,653 | Why it matters |
|---|---|---|---|
| Logic Function | Octal bus transceiver with 3-state outputs | Octal D-type transparent latch with 3-state outputs | Defines the core function; a transceiver buffers and directionally passes data, while a latch captures and holds data, so they are not functionally interchangeable. |
| Direction Control | Bidirectional via DIR pin (A-to-B or B-to-A) | Unidirectional (data flows D-to-Q only) | Determines whether the device can pass signals in both directions or only one, affecting bus architecture and wiring. |
| Data Storage / Latch | No storage; combinational pass-through | Transparent D-type latch with LE control | A latch can hold data when disabled, enabling temporary storage; a transceiver cannot, which changes timing and system behavior. |
| Control Inputs | OE (output enable) and DIR (direction) | OE (output enable) and LE (latch enable) | Different control pins mean different drive logic and PCB routing; substituting one for the other requires control signal redesign. |
| Number of Channels | 8 | 8 | Both handle 8 bits, so bus width compatibility is maintained between the two devices. |
| Output Type | 3-state | 3-state | 3-state outputs allow bus sharing by disconnecting the device; both support this, which is important for shared data buses. |
| Supply Voltage (VCC) | 4.5 V to 5.5 V | 4.5 V to 5.5 V | Both operate in the standard 5 V TTL-compatible range, so power supply compatibility is preserved. |
| Logic Family | HCT (High-speed CMOS, TTL-compatible) | HCT (High-speed CMOS, TTL-compatible) | Same logic family ensures compatible input thresholds, output levels, and noise margins when interfacing with TTL logic. |
| Package | SOIC-20 (D package) | SOIC-20 (D package) | Identical package and pin count allow the same PCB footprint, though pin functions differ and must be verified. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Matching temperature ranges ensure both parts suit the same environmental conditions and reliability requirements. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT245D | 74HCT373D,653 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HCT | 74HCT |
| Part Status | Active | Active |
| Logic Type | Transceiver, Non-Inverting | D-Type Transparent Latch |
| Circuit | - | 1:8 |
| Output Type | 3-State | Tri-State |
| Voltage - Supply | 4.5V ~ 5.5V | 4.5V ~ 5.5V |
| Independent Circuits | - | 1 |
| Delay Time - Propagation | - | 14ns |
| Current - Output High Low | 6mA, 6mA | 6mA, 6mA |
| Operating Temperature | -40°C ~ 125°C (TA) | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | 1 | - |
| Number of Bits per Element | 8 | - |
Frequently asked questions
What are the primary functional differences between the 74HCT245D and the 74HCT373D,653?
The 74HCT245D is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between two data buses. The 74HCT373D,653 is an octal D-type transparent latch with 3-state outputs, used for capturing and holding data. The 245D routes data (A to B or B to A) based on direction control, while the 373D stores data on the outputs when the latch enable is low and passes data transparently when high.
Are the 74HCT245D and 74HCT373D,653 pin-compatible?
No. Both use a 20-pin package (SOIC-20 for the 74HCT245D and SO-20 for the 74HCT373D,653), but their pin functions differ. The 245D has direction (DIR) and output enable (OE) pins, with data pins on both sides. The 373D has latch enable (LE) and output enable (OE) pins, with all inputs on one side and outputs on the other. They cannot be interchanged without circuit redesign.
Can the 74HCT245D and 74HCT373D,653 operate at the same supply voltage and logic levels?
Yes. Both are HCT-family devices that operate from a 4.5 V to 5.5 V supply and are TTL-voltage compatible, allowing direct interface with 5 V TTL logic. Their input thresholds and output drive characteristics are specified for the same nominal 5 V system.
Which device is suitable for bidirectional data bus buffering?
The 74HCT245D is the correct choice for bidirectional data bus buffering because it provides a direction control pin that selects A-to-B or B-to-A data flow. The 74HCT373D,653 is unidirectional and cannot reverse data flow; it only latches and buffers data from inputs to outputs.
Which device should be used to capture and hold data from a bus?
The 74HCT373D,653 should be used to capture and hold data. Its transparent latch feature allows data to flow through when LE is high and to be stored when LE goes low. The 74HCT245D does not have latch or storage capability; it only buffers or isolates data in real time.
Do both devices have 3-state outputs for bus isolation?
Yes. Both the 74HCT245D and 74HCT373D,653 feature 3-state outputs controlled by an output enable (OE) pin. When OE is inactive, the outputs enter a high-impedance state, effectively disconnecting the device from the bus.
What are the typical propagation delay and drive current specifications for these devices?
Both are standard HCT CMOS devices with typical propagation delays in the range of 10 ns to 20 ns at 5 V and output drive of ±6 mA (standard) or ±8 mA (bus-driver versions). Exact limits vary by manufacturer and must be verified from the specific datasheet for the 74HCT245D or 74HCT373D,653.
Can the 74HCT245D directly replace the 74HCT373D,653 in an existing design?
No. The two devices have different logic functions, pinouts, and control signals. A direct replacement is not possible without modifying the circuit to accommodate the different pin functions and data flow requirements. Functional equivalence would require external logic or a redesign.