MC74F243M - Quad Bus Transceiver, 3-State | onsemi | SOIC-14
Артикул: MC74F243M ✗ Снят с производстваMC74F243M Обзор
A bus transceiver is an interface IC that allows bidirectional data transfer between two buses or between a bus and a processor. In the logic IC hierarchy, the 74F243 is a specialized interface device - part of the broader 7400-series transistor-transistor logic (TTL) family - combining four driver circuits and four receiver circuits arranged in the same physical package so that data can flow from the A bus to the B bus or from the B bus to the A bus under the control of separate enable inputs.
Key features of the MC74F243 include four independent bus transceiver channels, 3-STATE outputs that effectively disconnect the device from the bus when disabled, and separate direction control (GAB and GBA type enables) for each transfer direction. The FAST Schottky TTL process delivers the fast edge rates expected of the 74F family, making the device suitable for backplane and inter-board data paths that outgrow slower 74LS-class transceivers.
Architecturally, each transceiver cell contains a driver with a 3-STATE output stage and a receiver path whose active state is selected by the enable pins. When an enable input is inactive, the corresponding outputs assume the high-impedance state, allowing multiple transceivers to share a common bus without bus contention.
Typical applications include bidirectional CPU memory-bus buffering, backplane data transceivers in industrial control systems, general-purpose 4-bit bus isolation, and legacy system maintenance where original TTL bus transceivers must be sourced for repair.
A key design consideration is that FAST TTL devices consume more power than CMOS alternatives; verify the drive and thermal requirements of your bus before selecting 74F over 74LS or 74HC parts.
This page consolidates sourcing availability, packaging details, and practical design notes for the MC74F243M in one place, complementing the manufacturer datasheet with drop-in replacement guidance not found on distributor pages.
Аналоги без доработки для MC74F243M — тот же корпус, pin-to-pin совместимость. Компоненты в других корпусах, требующие переработки PCB, исключены.
Для этого товара нет аналогов без доработки.
Запросить аналогиMC74F243M Характеристики
| Функция | Quad Bus Transceiver with 3-STATE Outputs |
| Logic Family | 74F (FAST Schottky TTL) |
| Number of Channels | 4 (Quad) |
| Тип выхода | 3-STATE |
| Direction Control | Separate enables for A-to-B and B-to-A transfer |
| Корпус | SOIC-14 |
| Тип монтажа | Surface Mount |
| Категория | Interface - Specialized |
| Статус RoHS | RoHS (per distributor listing) |
Руководство по цоколевке MC74F243M в корпусе soic-14
Цоколевка для MC74F243M (корпус soic-14). Нумерация выводов, функции и схемы подключения определены в техническом описании производителя. Обратитесь к нему для точного посадочного места и рекомендаций по пайке.
Нет подробных данных о распиновке для MC74F243M.
Обратитесь к даташиту для полной конфигурации выводов.
Типичное применение
MC74F243M подходит для 6 применениеs: CPU Memory Bus Buffering, Industrial Backplane Data Transfer, 4-Bit Bus Isolation and Direction Steering, Legacy TTL System Repair and Maintenance, Bidirectional Data Acquisition Front Ends, Inter-Board Data Handshaking in Communication Chassis.
CPU Memory Bus Buffering
The MC74F243M is used to buffer bidirectional processor data buses, where its four channels cover nibble-wide or bit-sliced data paths and its 3-STATE outputs release the bus to other masters during DMA or shared-memory arbitration. The 74F FAST Schottky process provides the short propagation delays required to keep setup and hold timing satisfied at legacy bus clock rates, and the separate enables let system control logic steer data from the CPU side to the memory side or in reverse under software or hardware direction control. In a typical microprocessor board, two or more MC74F243 devices in parallel form a full 8-bit or wider transceiver bank, each device isolating its slice when the bus is idle. Because the device is TTL-technology, designers must account for its static supply current, which is higher than CMOS equivalents, and ensure the power supply and decoupling network support FAST TTL switching surges during simultaneous bus transitions.
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Industrial Backplane Data Transfer
In industrial control backplanes, the MC74F243M transfers control and data signals between plug-in cards while its 3-STATE outputs allow many cards to share common backplane lines without contention. The separate direction-enable scheme matches the master/slave architecture typical of industrial bus controllers: one enable is driven by the bus-master grant signal and the other by the card's own transmitter-enable, so exactly one transceiver drives any given line at any time. The FAST TTL output drive comfortably meets the DC loading of heavily populated backplanes with multiple receiver taps. Designers mounting the SOIC-14 package on industrial cards should decouple each device with a 0.1 uF ceramic capacitor placed within a few millimeters of the VCC pin and provide a solid ground return, since simultaneous switching of four TTL outputs produces current spikes that can disturb nearby analog circuitry on mixed-signal industrial boards.
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4-Bit Bus Isolation and Direction Steering
General-purpose 4-bit bus isolation is one of the most common uses of the 74F243 function: the device electrically separates two sections of a digital system while allowing a controller to connect them on demand in either direction. When both enables are inactive, the 3-STATE outputs present a high impedance on both buses, letting the MC74F243M act as an electronic switch that isolates a failing or reconfigurable subsystem. The FAST Schottky technology ensures the isolation and connection transitions occur with minimal propagation delay, preserving timing budgets in tightly scheduled state machines. Designers should sequence the enables so that the previously active direction is released before the opposite direction is enabled, avoiding momentary bus contention between the two output groups. Pull-up or pull-down resistors on the enable pins guarantee a defined isolation state during power-up, before control logic has initialized its output drivers.
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Legacy TTL System Repair and Maintenance
The dominant modern use of the MC74F243M is repairing and maintaining legacy equipment - industrial machines, avionics, test instrumentation, and telecommunications gear - whose boards were designed around 74F TTL bus transceivers. Because onsemi discontinued the part, authorized-aftermarket units from Rochester Electronics are the standard sourcing route, providing new manufacture to original specifications rather than reclaimed scrap. Maintenance engineers value the exact 74F electrical behavior: replacing with a different logic family in a repair can shift edge rates enough to expose latent timing faults, so like-for-like replacement with a true 74F243 avoids re-characterizing the system. When sockets are present, the DIP-suffix variant of the same die can be used; for surface-mount boards the SOIC-14 MC74F243M matches the original land pattern directly with no footprint modification required.
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Bidirectional Data Acquisition Front Ends
In measurement and data-acquisition racks, the MC74F243M buffers the bidirectional control/status bus between an acquisition controller and multiple instrument modules. The transceiver carries command words from controller to module and status or data words back, with the 3-STATE capability letting dozens of modules share one status bus. The FAST TTL input thresholds provide defined noise margins in the electrically noisy environment of switching power supplies and relays typical of instrument racks, and the 74F speed keeps command-response latency low across multi-slot systems. Design considerations include keeping backplane stub lengths short to control signal reflections at TTL edge rates, distributing decoupling capacitance along the bus, and verifying that total receiver loading across all tapped modules stays within the FAST TTL fan-out specification published in the manufacturer datasheet electrical characteristics table.
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Inter-Board Data Handshaking in Communication Chassis
Communication chassis that predate modern serial fabrics often move parallel data between line cards and a control card through TTL bus transceivers, and the MC74F243M serves exactly this role with its four bidirectional channels and direction-control enables. The device sits between the card connector and the card's local logic, presenting the 3-STATE outputs to the shared backplane so only the addressed card drives, and its FAST Schottky delays support the parallel-bus clock rates used in these chassis. Because the part is surface-mount SOIC-14, it fits the dense card layouts of communication equipment without through-hole processes. Engineers maintaining such systems should confirm the enable polarity against the manufacturer function table before fitting replacements, since mis-driven enables are the most common field failure mode observed with bus transceiver repairs, resulting in two transceivers driving one backplane line simultaneously.
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Сводка рекомендуемых товаров
Справочные инженерные данные для MC74F243M — сравнение, рекомендации по проектированию и информация о соответствии.
Руководство по выбору
Сравнение с аналогами
| Параметр | Этот товар |
|---|---|
| Function | Quad bus transceiver, 3-STATE outputs |
| Logic Family | 74F (FAST Schottky TTL) |
| Package | SOIC-14 |
| Brand | onsemi (via Rochester Electronics aftermarket) |
| Lifecycle Status | Discontinued; authorized aftermarket supply |
| RoHS Status | RoHS compliant per distributor listing |
Ключевые отличия
- FAST Schottky TTL speed in a TTL-native bus transceiver (против 74LS243 family parts)
- Exact like-for-like replacement for 74F-era boards (против 74HC243 (CMOS) parts)
- Authorized-aftermarket new manufacture rather than reclaimed stock (против gray-market used inventory)
Заметки по проектированию
Never enable both transfer directions of the MC74F243M at the same time on a shared bus: driving the A-to-B and B-to-A enables active simultaneously causes both output groups to contend on the same lines, producing excessive current flow and possible device damage. Sequencing the enables so one direction releases (enters 3-STATE) before the other activates is the correct practice. Also add pull-up or pull-down resistors on the enable pins so the transceiver stays in a defined isolation state during power-up, before the system controller's direction-control outputs have initialized.
Place a 0.1 uF ceramic decoupling capacitor within a few millimeters of the MC74F243M VCC pin, with a solid ground return to the plane. FAST Schottky TTL outputs switch quickly and draw current spikes when all four channels change state together, so a shared or long decoupling trace can let rail noise propagate to neighboring devices. On backplane applications, keep the traces between the transceiver and the connector stub short and consider small series resistors at the bus side to damp reflections caused by the fast TTL edge rates over long shared lines.
74F TTL technology consumes considerably more static and dynamic supply current than CMOS equivalents such as the 74HC243. When repairing or retrofitting boards, verify that the power supply headroom and thermal budget still hold if multiple 74F transceivers are installed, and estimate power from the ICC values in the manufacturer datasheet rather than assuming CMOS-level figures. Estimated: if the datasheet ICC per device is on the order of tens of milliamps, a bank of four transceivers adds a meaningful load that the original supply must already have been designed for - substituting more 74F parts than the original design requires can exceed regulator capacity.
Информация о соответствии
RoHS compliance indicated by distributor listings (JLCPCB parts library). Other compliance attributes not stated in listings; confirm with supplier documentation.