MC74F85M - 4-Bit Magnitude Comparator | onsemi
MPN: MC74F85M ✓ ActiveMC74F85M Overview
A magnitude comparator is a combinational logic IC that evaluates the numerical relationship between two unsigned multibit operands. The MC74F85M sits within the hierarchy of digital comparator, combinational logic, logic IC, and integrated circuit categories. By presenting greater-than, equal-to, and less-than results in parallel, it reduces the number of gates, latches, and software operations otherwise needed to determine the relationship between two values.
The principal feature is expansion capability: the 74F85 function can be extended to almost any operand length. Its inputs accept binary, BCD, or other monotonic code relationships, while the output structure identifies three possible magnitude states. High-impedance NPN base inputs are listed as a feature of the related 74F85 family, supporting practical interfacing in TTL systems. These characteristics make the comparator useful where multi-level ordering decisions must be resolved quickly and deterministically.
Operationally, the three outputs support comparator cascading. When multiple four-bit sections are used, the upper section can use the lower section's result as an additional comparison input, allowing an eight-bit, twelve-bit, or wider magnitude decision. This architecture is faster and less complex than building a complete comparator from individual gate networks. The associated 74F85 description specifically identifies expansion to almost any length as a core capability.
Typical applications include binary and BCD value comparison, conditional branch generation, address and priority arbitration, sequence controllers, sorting networks, and industrial logic systems. The comparator can also support retrofits of legacy TTL boards because the MC74F85 function is associated with the established Fast Schottky TTL family and commonly documented under the 74F85 designation.
Designers should confirm the exact package, pin assignment, supply voltage, input levels, output timing, and propagation-delay limits for the MC74F85M before PCB release. Cascaded designs must allocate the additional comparison inputs correctly and route output states without creating contention. Because legacy logic may use different TTL families, input and output compatibility should be checked against the actual system levels rather than inferred from the comparator function alone.
This product overview synthesizes the verified function, expansion behavior, package uncertainty, sourcing status, and practical implementation considerations for engineers comparing the MC74F85M with other 74F85-compatible implementations. It also identifies the electrical details that must be checked in the manufacturer datasheet before qualification or layout approval.
Drop-in alternatives for MC74F85M — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
No drop-in alternatives available for this product.
Request AlternativesMC74F85M Maximum Ratings & Electrical Characteristics
| Comparator Type | 4-bit magnitude comparator |
| Number of Data Input Words | 2 words |
| Data Width per Input Word | 4 bits |
| Magnitude Result Outputs | 3 outputs |
| Supported Code Types | Binary, BCD, and other monotonic codes |
| Logic Family | Fast Schottky TTL |
| Input Structure | High-impedance NPN base inputs |
| Expansion Capability | Expandable to almost any comparison length |
MC74F85M standard Pin Configuration Guide
Pin configuration for MC74F85M (standard package). This analog component features input, output, and power supply pins. Refer to the manufacturer datasheet for offset null, compensation, and enable pin configurations. Ideal for signal conditioning and amplifier circuits.
No detailed pinout data available for MC74F85M.
Refer to the datasheet for full pin configuration.
Typical Applications
MC74F85M is suitable for 6 applications: Binary Magnitude Comparison, BCD Code Comparison, Multibit Comparator Cascading, Priority and Arbitration Control, Legacy TTL Control-System Retrofit, Sorting and Sequence Selection.
Binary Magnitude Comparison
The MC74F85M provides a direct hardware solution for comparing two four-bit binary operands and generating greater-than, equal-to, and less-than results. This is useful when a controller must decide whether a measured code, counter value, or arithmetic result exceeds a reference without performing a multi-step software comparison. The documented 74F85 architecture supports binary and other monotonic code systems, while three separate outputs allow downstream gates to act directly on the relationship. Confirm input thresholds, output polarity, and timing in the manufacturer datasheet before operating the logic near TTL transition regions or high fan-out.
Recommended
BCD Code Comparison
The MC74F85M can compare BCD values because the 74F85 function accepts binary, BCD, and other monotonic code relationships. It suits decade-counter and display-processing systems in which a decoded decimal value must determine whether it is above, equal to, or below a programmed threshold. Using the dedicated greater-than, equal-to, and less-than outputs simplifies control of alarm, gating, and sequencing logic. Designers should still account for invalid BCD states, input settling time, and unused expansion inputs according to the device datasheet rather than assuming that the outputs cover every fault condition.
Recommended
Multibit Comparator Cascading
The MC74F85M can serve as a building block for wider comparisons by cascading four-bit sections. The least-significant section determines the relationship between the lowest-order bits, and its result becomes part of the decision made by the next section. The documented ability to expand to almost any length makes this architecture useful for eight-bit, twelve-bit, and larger legacy control systems. The PCB must reserve the required comparison and expansion pins, while logic designers must implement polarity and tie-off rules exactly as specified in the manufacturer pin table.
Recommended
Priority and Arbitration Control
The MC74F85M fits arbitration networks that must select between request sources according to their coded priority. Two four-bit request identifiers can be compared, and the greater-than, equal-to, or less-than result can enable a corresponding grant path. This avoids the propagation delay and component count of a large priority-encoder implementation when the system already uses TTL-style logic levels. For reliable arbitration, validate setup and output timing, ensure that grant signals remain mutually exclusive, and follow the device’s fan-out and output-drive constraints.
Recommended
Legacy TTL Control-System Retrofit
The MC74F85M is relevant to maintenance and modernization of legacy TTL control systems because its documented function is part of the Fast Schottky TTL 74F85 family. It can reproduce three magnitude decisions without rebuilding the original comparator from discrete gates, helping preserve board behavior during repair or controlled redesign. Before installation, compare the MC74F85M package and suffix with the removed device, verify supply compatibility, and test every input and output state. Backward functional equivalence does not guarantee identical timing, noise margins, or thermal performance across the complete system.
Recommended
Sorting and Sequence Selection
The MC74F85M can implement comparison stages in sorting networks, threshold controllers, and sequence-selection logic. Its three outputs allow a system to determine whether a current code is above, equal to, or below a stored or incoming reference and then advance, hold, or reset a state machine. The high-impedance NPN base input feature associated with the 74F85 family may assist TTL interfacing, but the actual thresholds and loading must be checked against the exact device data. Place the comparator near its connected logic and preserve the specified unused-pin treatment to reduce contention and noise susceptibility.
Recommended
Recommended Products Summary
Engineering reference data for MC74F85M — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product |
|---|---|
| Brand | onsemi |
| Comparator Type | 4-bit magnitude comparator |
| Input Words | 2 |
| Data Width | 4 bits per word |
| Magnitude Outputs | 3 |
| Supported Codes | Binary, BCD, and other monotonic codes |
| Logic Family | Fast Schottky TTL |
| Expansion Capability | Expandable to almost any comparison length |
Key Differentiators
- Documented expansion architecture (vs 74F85)
- Three explicit magnitude results (vs Generic single-output comparator)
- Support for multiple numeric code formats (vs Binary-only comparator)
Design Notes
Do not treat the generic 74F85 name as proof that every MC74F85M order suffix has the same package or electrical ratings. Confirm the exact suffix, pin drawing, supply range, input thresholds, output levels, and temperature grade against the manufacturer documentation before replacing a component. Also verify whether unused expansion pins require defined logic levels; leaving them uncontrolled can create unnecessary switching activity in a TTL system.
Keep comparator inputs and outputs short, especially in cascaded implementations where several sections communicate magnitude results. Route the supply and ground pins directly to their respective planes, place required bypass components at the device, and avoid sharing narrow return paths with high-current switching nodes. Consistent grounding helps preserve the input thresholds needed for reliable binary or BCD decision-making.
Account for propagation delay when cascading sections and when comparator results feed sequential control logic. The least-significant section must settle before the next section makes its final decision, and additional margin may be needed when fan-out or wiring length is high. Use the timing values from the manufacturer datasheet for the exact MC74F85M configuration instead of estimating performance from a generic TTL family.
Compliance Information
The verified product summary does not state compliance or automotive-qualification results for the exact MC74F85M suffix. Obtain current manufacturer declarations before controlled production release.
