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Home > Products > Integrated Circuits (ICs) > Logic > FIFOs Memory

Texas Instruments SN74ABT7820-25PN

Name: SN74ABT7820-25PN
Brand: Texas Instruments
SKU: SN74ABT7820-25PN
Price: 2.40 USD
Availability: InStock
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Part No.:: SN74ABT7820-25PN

Manufacturer:: Texas Instruments

Category:: FIFOs Memory

Package:: 80-LQFP

Datasheet:: SN74ABT7820-25PN.pdf

Description:: IC FIFO ASYNC 512X18X2 80LQFP

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Product details

Overview

SN74ABT7820-25PN from Texas Instruments is a strobed bidirectional first-in, first-out (FIFO) memory IC with two independent 512 × 18-bit FIFO buffers operating in opposite directions, supporting up to 40 MHz clock rate, 12 ns access time at 50-pF load, and programmable almost-full/almost-empty flags. It serves as a high-speed data flow controller in bus arbitration and protocol bridging applications between asynchronous subsystems.

For engineers reviewing the SN74ABT7820-25PN datasheet, SN74ABT7820-25PN pinout, SN74ABT7820-25PN application, or SN74ABT7820-25PN equivalent, this page delivers verified functional identity, timing-critical specifications, validated 80-pin TQFP (PN) package mapping, confirmed dual-FIFO architecture, and real-world interface use cases - all derived from TI SCAS206D Rev. April 1998 production data.

Technical Context

The SN74ABT7820-25PN implements two fully independent 512-word × 18-bit FIFOs with separate load clocks (LDCKA/LDCKB), unload clocks (UNCKA/UNCKB), and reset controls (RSTA/RSTB), enabling simultaneous bidirectional data buffering without shared timing constraints. Each FIFO supports programmable AF/AE flag offsets (X/Y) via PENA/PENB latching of A0–A7/B0–B7 during reset.

Its bus-transceiver core integrates GAB/GBA output enables and SAB/SBA read-select logic to route either real-time or FIFO-stored data between Port-A (A0–A17) and Port-B (B0–B17), eliminating multiplexer glitches during mode transitions per Figure 1. All control and flag signals operate at TTL-compatible voltage levels (VIH = 2 V, VIL = 0.8 V) across 0°C to 70°C.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory depth × width × banks	512 × 18 × 2 - Two independent FIFOs, each storing 512 words of 18-bit parallel data for full-duplex buffering.
Max clock frequency	40 MHz - Validated maximum operational clock rate for LDCKA/UNCKA and LDCKB/UNCKB under recommended conditions.
Access time	12 ns - Propagation delay from clock edge to valid output data with 50-pF capacitive load, critical for timing closure.
Supply voltage range	4.5 V to 5.5 V - Operates within standard 5-V TTL/CMOS rail; not compatible with 3.3-V or mixed-voltage systems without level shifting.
Operating temperature	0°C to 70°C - Commercial-grade thermal range; unsuitable for extended industrial (-40°C to 85°C) or automotive applications.
Programmable AF/AE offset	0–255 words per FIFO - Enables custom almost-full/almost-empty thresholds via PENA/PENB latching, avoiding fixed-threshold limitations.
Flag outputs	EMPTYA/FULLA/HFA/AF/AEA and EMPTYB/FULLB/HFB/AF/AEB - Eight dedicated status flags provide real-time FIFO state visibility for DMA and interrupt-driven control.

Pinout & Package

SN74ABT7820-25PN is housed in an 80-pin Thin Quad Flat Package (TQFP, PN), measuring 12 mm × 12 mm with 0.5-mm pitch. Pin numbering follows standard counter-clockwise orientation from top-left corner (Pin 1) in top-view layout.

Pin/Terminal	Circuit Role	Design Meaning
A0–A17	Port-A bidirectional data bus	18-bit parallel I/O port for side A; connects directly to host processor or peripheral data bus.
B0–B17	Port-B bidirectional data bus	18-bit parallel I/O port for side B; electrically isolated from Port-A except through FIFO or transceiver paths.
LDCKA / LDCKB	FIFO write clock input	Low-to-high transition writes data into FIFO A or B only when FULLx is high; first word bypasses FIFO to output.
UNCKA / UNCKB	FIFO read clock input	Low-to-high transition reads data from FIFO A or B only when EMPTYx is high; output remains valid until next clock.
RSTA / RSTB	Asynchronous FIFO reset	Active-low signal forces EMPTYx low, FULLx high, HFx low, and AF/AEx high - clearing FIFO state without power cycle.
PENA / PENB	AF/AE offset programming enable	Low during LDCKx pulse latches A0–A7/B0–B7 as X/Y offset values; must be asserted before first write post-reset.
SAB / SBA	Bus read-source select	Selects whether Port-B/Port-A outputs deliver real-time data (cross-bus) or FIFO-stored data (buffered path).
GAB / GBA	Port output enable	High enables drivers on Port-B/Port-A; low places outputs in high-impedance state for bus sharing.
AF/AEA / AF/AEB	Programmable almost-full/almost-empty flag	Open-collector output active high when FIFO contains ≤X words (almost empty) or ≥(512−Y) words (almost full).
EMPTYA / EMPTYB	FIFO empty status	Active-low flag indicating zero valid words stored; used to gate read operations and prevent underflow.
FULLA / FULLB	FIFO full status	Active-low flag indicating 512 words stored; used to gate write operations and prevent overflow.
HFA / HFB	Half-full status	Active-high flag set when ≥256 words present; useful for flow control hysteresis and buffer-level monitoring.

Key Features

Feature	Design Value
Dual independent FIFO architecture	Enables concurrent bidirectional data flow without inter-FIFO timing coupling or arbitration overhead.
Programmable AF/AE offset (0–255)	Allows dynamic tuning of buffer warning thresholds to match system-specific latency, burst size, and interrupt response requirements.
Glitch-free bus management	SAB/SBA control logic eliminates transient invalid states during real-time ↔ FIFO mode switching, ensuring deterministic data routing.
12 ns access time @ 50 pF	Supports tight timing budgets in high-speed backplane and local bus interfaces operating up to 40 MHz.
Eight dedicated status flags	Provides complete real-time visibility into both FIFO states (empty/full/half-full/almost-full/almost-empty) for autonomous DMA and firmware control.

Applications

PCI-to-ISA Bridge Buffering	Real-Time DSP Data Pipeline
Use Scenario: Bridging PCI bus (33 MHz, 32-bit) to legacy ISA (8 MHz, 16-bit) while maintaining data coherency across clock domains. IC Role / Device Role / Timing Role: SN74ABT7820-25PN acts as dual-asynchronous FIFO buffer - one FIFO absorbs PCI bursts, the other feeds ISA transfers - decoupling timing and preventing overrun/underrun. Use Value: Eliminates need for complex handshake logic or software polling; 512-word depth accommodates worst-case PCI burst (128 DWORDs) with margin for latency jitter.	Use Scenario: Streaming sensor data from ADC to DSP core while simultaneously feeding processed results to DAC or display controller. IC Role / Device Role / Timing Role: SN74ABT7820-25PN provides full-duplex pipeline staging - FIFO A ingests raw samples, FIFO B outputs processed frames - synchronized via independent LDCK/UNCK clocks. Use Value: Enables deterministic latency control; programmable AF/AE flags trigger DMA reloads at precise buffer occupancy points, minimizing CPU intervention.
Industrial Fieldbus Protocol Converter	Legacy Memory Expansion Interface
Use Scenario: Translating Modbus RTU (serial) to EtherNet/IP (parallel packetized) in gateway hardware requiring deterministic framing and error recovery. IC Role / Device Role / Timing Role: SN74ABT7820-25PN buffers incoming serial frame fragments in FIFO A and assembles outbound Ethernet packets in FIFO B, using SAB/SBA to switch between real-time UART RX/TX and buffered packet payload paths. Use Value: Prevents frame loss during protocol translation; half-full flags (HFA/HFB) signal firmware to initiate packet assembly before buffer saturation.	Use Scenario: Extending address/data bus of microcontroller with external SRAM or flash where native bus timing cannot meet memory access requirements. IC Role / Device Role / Timing Role: SN74ABT7820-25PN operates as write-postponement and read-preload buffer - absorbing fast MCU writes into FIFO A and feeding slower memory reads from FIFO B - effectively widening setup/hold windows. Use Value: Enables use of standard 55-ns SRAM with sub-40-MHz MCU buses; 12 ns access time ensures no added latency in critical read paths.

PCI-to-ISA Bridge Buffering

Real-Time DSP Data Pipeline

Use Scenario: Bridging PCI bus (33 MHz, 32-bit) to legacy ISA (8 MHz, 16-bit) while maintaining data coherency across clock domains.

IC Role / Device Role / Timing Role: SN74ABT7820-25PN acts as dual-asynchronous FIFO buffer - one FIFO absorbs PCI bursts, the other feeds ISA transfers - decoupling timing and preventing overrun/underrun.

Use Value: Eliminates need for complex handshake logic or software polling; 512-word depth accommodates worst-case PCI burst (128 DWORDs) with margin for latency jitter.

Use Scenario: Streaming sensor data from ADC to DSP core while simultaneously feeding processed results to DAC or display controller.

IC Role / Device Role / Timing Role: SN74ABT7820-25PN provides full-duplex pipeline staging - FIFO A ingests raw samples, FIFO B outputs processed frames - synchronized via independent LDCK/UNCK clocks.

Use Value: Enables deterministic latency control; programmable AF/AE flags trigger DMA reloads at precise buffer occupancy points, minimizing CPU intervention.

Industrial Fieldbus Protocol Converter

Legacy Memory Expansion Interface

Use Scenario: Translating Modbus RTU (serial) to EtherNet/IP (parallel packetized) in gateway hardware requiring deterministic framing and error recovery.

IC Role / Device Role / Timing Role: SN74ABT7820-25PN buffers incoming serial frame fragments in FIFO A and assembles outbound Ethernet packets in FIFO B, using SAB/SBA to switch between real-time UART RX/TX and buffered packet payload paths.

Use Value: Prevents frame loss during protocol translation; half-full flags (HFA/HFB) signal firmware to initiate packet assembly before buffer saturation.

Use Scenario: Extending address/data bus of microcontroller with external SRAM or flash where native bus timing cannot meet memory access requirements.

IC Role / Device Role / Timing Role: SN74ABT7820-25PN operates as write-postponement and read-preload buffer - absorbing fast MCU writes into FIFO A and feeding slower memory reads from FIFO B - effectively widening setup/hold windows.

Use Value: Enables use of standard 55-ns SRAM with sub-40-MHz MCU buses; 12 ns access time ensures no added latency in critical read paths.

Equivalent & Alternatives

The following parts are listed as comparable options for similar FIFO memory applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
IDT72V251L15PF	3.3-V LVCMOS operation, 1024 × 18 depth, 10 ns access, JTAG boundary scan support	Requires level-shifting for 5-V systems; deeper buffer suits longer latency bridges but consumes more power	Preferred for new 3.3-V designs needing higher density and IEEE 1149.1 testability
SN74ACT7820-25PN	Same pinout and function, but ACT-family CMOS process: lower ICC (15 mA vs. 95 mA), reduced noise, 4.5–5.5 V supply	Lower power and EMI; identical timing and feature set makes it drop-in for noise-sensitive or thermally constrained layouts	Direct functional replacement where power efficiency or signal integrity outweighs ABT-series drive strength needs

Compared with IDT72V251L15PF and SN74ACT7820-25PN, the SN74ABT7820-25PN offers superior drive capability (24-mA sink) for heavy bus loading and legacy 5-V TTL compatibility, while retaining identical 80-pin TQFP footprint and dual-FIFO control architecture - making it optimal for retrofitting or maintaining existing 5-V industrial bus systems.

Availability

SN74ABT7820-25PN is available at Aetrix Electronics and suitable for PCI-to-ISA bridging, real-time DSP pipelines, industrial fieldbus protocol conversion, legacy memory expansion interfaces, and asynchronous bus arbitration requiring stable component supply across long-lifecycle embedded programs.

Supply support for SN74ABT7820-25PN includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.

The SN74ABT7820-25PN belongs to TI's Widebus™ family of advanced BiCMOS bus-interface devices, engineered specifically for high-speed, low-latency data buffering and asynchronous domain crossing in commercial-grade computing and industrial control systems.

FAQ

What is the exact memory configuration of the SN74ABT7820-25PN?

The SN74ABT7820-25PN contains two physically and electrically independent FIFO memories, each configured as 512 words × 18 bits. This yields a total buffering capacity of 18,432 bits (9,216 bits per FIFO), with separate clock, reset, and flag signals for each bank. No shared memory space or cross-FIFO addressing exists - the architecture strictly enforces bidirectional isolation.

Does the SN74ABT7820-25PN support 3.3-V operation?

No, the SN74ABT7820-25PN is specified only for 4.5 V to 5.5 V supply operation per its Recommended Operating Conditions table. Applying 3.3 V will result in non-functional behavior, including failure to assert FULL/EMPTY flags correctly and inability to latch data on LDCK/UNCK edges. For 3.3-V systems, consider the pin-compatible SN74ACT7820-25PN or IDT72V251L15PF instead.

How are the almost-full/almost-empty flags programmed on the SN74ABT7820-25PN?

The SN74ABT7820-25PN allows independent programming of AF/AEA and AF/AEB offsets via PENA and PENB. After reset, asserting PENA low during a LDCKA rising edge latches A0–A7 as both X (almost-empty) and Y (almost-full) values; a second LDCKA edge reprograms Y only. Default offset is X = Y = 128 if PENA/PENB remain high. Programming occurs before any data write and does not affect FIFO contents.

What is the meaning of the "-25" suffix in SN74ABT7820-25PN?

The "-25" in SN74ABT7820-25PN denotes the speed grade: it guarantees maximum clock frequency of 40 MHz and 12 ns access time under standard test conditions (VCC = 5 V, CL = 50 pF, TA = 25°C). This distinguishes it from -15 (67 MHz), -20 (50 MHz), and -30 (33 MHz) variants - all sharing identical pinout, functionality, and package (PN), but differing in timing performance.

Can the SN74ABT7820-25PN be used for single-directional buffering only?

Yes, the SN74ABT7820-25PN supports single-directional use by configuring one FIFO for write-only and the other for read-only operation, or by tying SAB/SBA to fixed logic levels. For example, holding SAB = L and SBA = L routes real-time A↔B data without FIFO involvement, while GAB/GBA enables/disables transceiver drivers - allowing flexible reuse as a pure bus transceiver or unidirectional buffer depending on control signal states.

SN74ABT7820-25PN Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74ABT

Package/Case:: 80-LQFP

Packaging:: Tray

Product Status:: Obsolete

Programmable:: Not Verified

Memory Size:: 18K (512 x 18 x 2)

Function:: Asynchronous

Data Rate:: 40MHz

Access Time:: 15ns

Voltage - Supply:: 4.5 V ~ 5.5 V

Current - Supply (Max):: 95mA

Bus Directional:: Bi-Directional

Expansion Type:: -

Programmable Flags Support:: Yes

Retransmit Capability:: No

FWFT Support:: No

Operating Temperature:: 0°C ~ 70°C

Mounting Type:: Surface Mount

Supplier Device Package:: 80-LQFP (12x12)

SN74ABT7820-25PN FAQ

1.How can I place an order for SN74ABT7820-25PN through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74ABT7820-25PN on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74ABT7820-25PN reliable?

The price and inventory of SN74ABT7820-25PN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ABT7820-25PN is usually 5 days.

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Once your SN74ABT7820-25PN order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74ABT7820-25PN?

For technical support, including SN74ABT7820-25PN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ABT7820-25PN requirements.

6.How does Aetrix verify that SN74ABT7820-25PN is sourced from the original manufacturer or authorized distributors?

All SN74ABT7820-25PN products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74ABT7820-25PN meets industry standards.

7.What is the process for return or replacement of SN74ABT7820-25PN?

All SN74ABT7820-25PN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ABT7820-25PN, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74ABT7820-25PN part is unused and in its original packaging.

Return procedure for SN74ABT7820-25PN:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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