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

Texas Instruments SN74ACT3638-15PCB

Name: SN74ACT3638-15PCB
Brand: Texas Instruments
SKU: SN74ACT3638-15PCB
Price: 2.40 USD
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Part No.:: SN74ACT3638-15PCB

Manufacturer:: Texas Instruments

Category:: FIFOs Memory

Package:: -

Datasheet:: SN74ACT3638-15PCB.pdf

Description:: IC FIFO 512X32 BI-DIRECTIONAL

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Product details

Overview

SN74ACT3638-15PCB from Texas Instruments is a clocked bidirectional FIFO memory IC with two independent 512 × 32 dual-port SRAM FIFOs, supporting asynchronous or coincident CLKA/CLKB up to 67 MHz, 11 ns access time, and mailbox-bypass registers for parallel data exchange in embedded inter-processor communication systems.

For engineers reviewing the SN74ACT3638-15PCB datasheet, SN74ACT3638-15PCB pinout, SN74ACT3638-15PCB application, or SN74ACT3638-15PCB equivalent, this page delivers verified timing behavior, flag synchronization logic, retransmit mode operation, mailbox register control, and PCB-package terminal mapping - all confirmed from TI SCAS228D (April 1998) production data.

Technical Context

The SN74ACT3638-15PCB implements two fully independent, clock-synchronized FIFOs (FIFO1 and FIFO2), each with 512 × 32-bit depth and separate read/write pointers, input-ready/output-ready flags, and programmable almost-full/almost-empty offsets. CLKA and CLKB operate asynchronously or coincidently, with all port-A flags (IRA, ORA, AFA, AEA) synchronized to CLKA and all port-B flags (IRB, ORB, AFB, AEB) synchronized to CLKB via two-stage flip-flop chains to suppress metastability.

It supports microprocessor interface control via CSA/CSB, W/RA/W/RB, ENA/ENB, and includes mailbox-bypass registers (Mail1/Mail2) with MBF1/MBF2 status flags, plus synchronous retransmit capability (RTM/RFM) for FIFO1 - enabling repeat reads from a user-marked location without disrupting write operations.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Depth × Width × Ports	512 × 32 × 2 - Two independent dual-port FIFOs, each buffering 512 words of 32-bit data bidirectionally between Port A and Port B.
Max Clock Frequency	67 MHz - Enables high-throughput data transfer in real-time interconnect applications such as DSP-to-ASIC bridging.
Read Access Time	11 ns - Guarantees fast data availability at output register after read-enable assertion, critical for tight-timing control loops.
Flag Synchronization	Two-stage sync per port - IRA/ORA/AFA/AEA tied to CLKA; IRB/ORB/AFB/AEB tied to CLKB - reduces metastability risk in asynchronous clock domain crossings.
Programmable Flag Offsets	X1/X2/Y1/Y2 registers - Allow runtime configuration of almost-empty (1–508 words) and almost-full (1–508 empty slots) thresholds via Port A writes or FS0/FS1 reset latching.
Retransmit Capability	FIFO1 only - RTM/RFM signals enable repeat reads from a marked position without affecting FIFO pointer progression or write integrity.
Operating Temperature	0°C to +70°C - Qualified for commercial-grade embedded systems including industrial controllers and communications equipment.

Pinout & Package

SN74ACT3638-15PCB uses a 120-pin Thin Quad Flat Package (TQFP), designated "PCB" in TI documentation, with exposed thermal pad (not electrically connected), 0.4 mm lead pitch, and JEDEC MO-140 compliant footprint.

Pin/Terminal	Circuit Role	Design Meaning
A0–A31	Port-A bidirectional data bus	32-bit I/O path for FIFO2 read/write and Mail2 register access; high-impedance when CSA or W/RA high.
B0–B31	Port-B bidirectional data bus	32-bit I/O path for FIFO1 read/write and Mail1 register access; high-impedance when CSB or W/RB low.
CLKA / CLKB	Free-running port clocks	Independent, continuous clocks synchronizing all Port-A and Port-B transfers; support asynchronous or coincident operation.
CSA / CSB	Port chip select inputs	Enable low-to-high CLKA/CLKB transitions for data transfer; force A0–A31/B0–B31 into high-Z when deasserted.
W/RA / W/RB	Port write/read direction controls	W/RA high = Port-A write; W/RB low = Port-B write - inverted logic ensures safe bus arbitration in shared-data environments.
ENA / ENB	Port enable inputs	Gate clock-triggered transfers: ENA/ENB must be high for CLKA/CLKB edges to initiate valid read/write cycles.
IRA / IRB	Input-ready flags (synchronized)	Low = FIFO full (IRA→FIFO1, IRB→FIFO2); used to throttle upstream writers; synchronized to CLKA/CLKB respectively.
ORA / ORB	Output-ready flags (synchronized)	High = valid data in output register (ORA→FIFO2, ORB→FIFO1); enables downstream readers; synchronized to CLKA/CLKB respectively.
MBA / MBB	Mailbox select inputs	High = route A0–A31/B0–B31 to Mail2/Mail1 register instead of FIFO output register - enables non-FIFO data exchange.
MBF1 / MBF2	Mailbox full flags	Low = Mail1/Mail2 register occupied; prevents overwrites; set low on write, cleared by corresponding port read with MBA/MBB high.
RST1 / RST2	Independent FIFO reset inputs	Asynchronous active-low resets requiring ≥4 CLKA+CLKB transitions; initialize pointers, flags, and offset registers; mandatory at power-up.
RTM / RFM	FIFO1 retransmit controls	RTM high + ORB high → mark current output as retransmit start; RFM high → restart retransmit sequence from marked location.
RDYA / RDYB	Composite ready outputs	RDYA = !IRA (W/RA=H) or !ORA (W/RA=L); RDYB = !IRB (W/RB=L) or !ORB (W/RB=H) - simplifies handshake logic in microprocessor interfaces.

Key Features

Feature	Design Value
Dual independent FIFO architecture	Enables simultaneous bidirectional buffering - e.g., Port A ↔ Host CPU, Port B ↔ Peripheral - without shared resource contention or arbitration logic.
Mailbox-bypass registers (Mail1/Mail2)	Provide dedicated 32-bit registers for initialization, command passing, or status reporting outside FIFO flow - eliminating need for external latch logic.
Programmable almost-full/almost-empty thresholds	Four offset registers (X1/X2/Y1/Y2) configurable via reset latching (FS0/FS1) or Port A writes - allows dynamic tuning of flow-control sensitivity in variable-bandwidth links.
Synchronous retransmit (FIFO1 only)	Supports deterministic replay of data blocks (≥3 words) from a marked location - essential for protocol recovery, debug trace replay, and firmware update verification.
Metastability-hardened flag synchronization	Two-stage flip-flop chains on all status flags ensure reliable cross-clock-domain signaling even under worst-case skew and jitter conditions.

Applications

Inter-Processor Communication	DSP-to-ASIC Data Bridge
Use Scenario: Two microcontrollers exchange command/status packets across isolated clock domains with no shared bus or arbitration logic. IC Role / Device Role / Timing Role: SN74ACT3638-15PCB acts as a dual-port, clock-domain-crossing FIFO buffer - absorbing timing mismatches while providing mailbox registers for control message handshaking. Use Value: Eliminates need for custom glue logic or software polling; guarantees lossless packet delivery with hardware-enforced flow control via IRA/IRB and ORA/ORB flags.	Use Scenario: A DSP streams processed audio frames to an ASIC-based encoder, while the ASIC returns metadata and error reports back to the DSP. IC Role / Device Role / Timing Role: SN74ACT3638-15PCB serves as a bidirectional streaming buffer - FIFO1 handles DSP→ASIC writes/ASIC→DSP reads; FIFO2 handles reverse-path metadata exchange. Use Value: Enables concurrent full-duplex streaming at 67 MHz; programmable almost-full flags prevent overflow during bursty encoder latency; retransmit mode aids debug trace capture.
Industrial PLC Backplane Interface	Legacy Bus Protocol Adapter
Use Scenario: A modern ARM-based controller interfaces with legacy 80C188-based I/O modules over a synchronous parallel bus with mismatched clock rates. IC Role / Device Role / Timing Role: SN74ACT3638-15PCB functions as a clock-isolated bridge - CLKA synchronized to ARM bus, CLKB to 80C188 bus; mailbox registers handle module address/configuration setup. Use Value: Absorbs clock skew and jitter; prevents data corruption during hot-swap or reset events; IRA/IRB flags provide hardware flow control compatible with legacy timing constraints.	Use Scenario: Converting between two incompatible parallel protocols - e.g., ISA-style memory-mapped I/O and VME-style dual-ported register access - in test equipment. IC Role / Device Role / Timing Role: SN74ACT3638-15PCB operates as a protocol-transparent, dual-clock FIFO adapter - using Mail1/Mail2 for protocol-specific control words and FIFOs for payload streaming. Use Value: Reduces FPGA gate count by offloading clock-domain crossing and handshaking; retransmit capability supports repeatable stimulus generation for compliance testing.

Inter-Processor Communication

DSP-to-ASIC Data Bridge

Use Scenario: Two microcontrollers exchange command/status packets across isolated clock domains with no shared bus or arbitration logic.

IC Role / Device Role / Timing Role: SN74ACT3638-15PCB acts as a dual-port, clock-domain-crossing FIFO buffer - absorbing timing mismatches while providing mailbox registers for control message handshaking.

Use Value: Eliminates need for custom glue logic or software polling; guarantees lossless packet delivery with hardware-enforced flow control via IRA/IRB and ORA/ORB flags.

Use Scenario: A DSP streams processed audio frames to an ASIC-based encoder, while the ASIC returns metadata and error reports back to the DSP.

IC Role / Device Role / Timing Role: SN74ACT3638-15PCB serves as a bidirectional streaming buffer - FIFO1 handles DSP→ASIC writes/ASIC→DSP reads; FIFO2 handles reverse-path metadata exchange.

Use Value: Enables concurrent full-duplex streaming at 67 MHz; programmable almost-full flags prevent overflow during bursty encoder latency; retransmit mode aids debug trace capture.

Industrial PLC Backplane Interface

Legacy Bus Protocol Adapter

Use Scenario: A modern ARM-based controller interfaces with legacy 80C188-based I/O modules over a synchronous parallel bus with mismatched clock rates.

IC Role / Device Role / Timing Role: SN74ACT3638-15PCB functions as a clock-isolated bridge - CLKA synchronized to ARM bus, CLKB to 80C188 bus; mailbox registers handle module address/configuration setup.

Use Value: Absorbs clock skew and jitter; prevents data corruption during hot-swap or reset events; IRA/IRB flags provide hardware flow control compatible with legacy timing constraints.

Use Scenario: Converting between two incompatible parallel protocols - e.g., ISA-style memory-mapped I/O and VME-style dual-ported register access - in test equipment.

IC Role / Device Role / Timing Role: SN74ACT3638-15PCB operates as a protocol-transparent, dual-clock FIFO adapter - using Mail1/Mail2 for protocol-specific control words and FIFOs for payload streaming.

Use Value: Reduces FPGA gate count by offloading clock-domain crossing and handshaking; retransmit capability supports repeatable stimulus generation for compliance testing.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
IDT72V2115L15PF	512 × 18 × 2, 3.3 V, 15 ns access, LVCMOS I/O, no mailbox registers or retransmit mode	Limited to 18-bit data paths; lacks mailbox bypass and synchronous retransmit - unsuitable for 32-bit control/data coexistence	Choose when lower voltage, smaller width, and simpler flag set suffice; avoid if 32-bit mailbox or retransmit is required.
ON Semiconductor NB3N502DR2G	Single 256 × 16 FIFO, 2.5 V, 10 ns, no dual-port or mailbox - designed for clock/data recovery, not inter-processor buffering	Not bidirectional; no second port or mailbox; no retransmit; insufficient depth/width for parallel processor links	Only viable for narrow, single-direction timing-critical paths - not a functional substitute for SN74ACT3638-15PCB's dual 32-bit FIFO architecture.

Compared with IDT72V2115L15PF and NB3N502DR2G, SN74ACT3638-15PCB uniquely delivers 32-bit dual-port buffering, integrated mailbox registers, and FIFO1 retransmit - making it irreplaceable in applications requiring deterministic bidirectional data exchange with embedded control messaging.

Availability

SN74ACT3638-15PCB is available at Aetrix Electronics and suitable for industrial PLC backplanes, DSP-to-ASIC bridging, and inter-processor communication systems requiring stable component supply, long-lifecycle support, and guaranteed pinout consistency across production batches.

Supply support for SN74ACT3638-15PCB 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in high-reliability timing and interface ICs.

The SN74ACT3638-15PCB belongs to TI's advanced CMOS FIFO memory product line, engineered specifically for robust, low-power, clock-domain-crossing data buffering in multi-processor and mixed-signal systems.

FAQ

What is the function of the RTM and RFM pins on the SN74ACT3638-15PCB?

The RTM (Retransmit Mode) and RFM (Read From Mark) pins enable synchronous retransmission from FIFO1. When RTM is high and ORB is high, a rising edge on CLKB marks the current output word as the retransmit start point. Subsequently, asserting RFM high triggers a rising CLKB edge to reload that marked word into the output register - allowing repeat reads without disturbing FIFO write operations or pointer states. This functionality is exclusive to FIFO1 and is documented in TI SCAS228D Section 3.

Does the SN74ACT3638-15PCB support independent reset of its two FIFOs?

Yes, the SN74ACT3638-15PCB provides fully independent reset control via RST1 (for FIFO1) and RST2 (for FIFO2). Each requires ≥4 low-to-high transitions on both CLKA and CLKB while the respective RST input is low. The low-to-high transition of RST1 or RST2 latches FS0/FS1 values for offset programming and initializes all internal pointers, flags (IRA, ORA, AFA, AEA, etc.), and mailbox flags (MBF1, MBF2). Power-up reset is mandatory before writing to either FIFO.

How are the almost-full and almost-empty flag offsets programmed on the SN74ACT3638-15PCB?

Offset registers X1/X2 (almost-empty) and Y1/Y2 (almost-full) are programmed either during reset via FS0/FS1 latching (selecting preset values 8, 16, or 64) or dynamically from Port A. For Port A programming, both RST1 and RST2 must be asserted simultaneously with FS0=FS1=low; then the first four writes to FIFO1 load Y1, X1, Y2, X2 sequentially using A8–A0 bits. Valid offset values range from 1 to 508, and all offsets are synchronized to their respective port clocks.

What is the role of the MBA and MBB pins on the SN74ACT3638-15PCB?

MBA (Mailbox A) and MBB (Mailbox B) are port-select inputs that determine whether A0–A31 or B0–B31 present FIFO output-register data or mailbox-register data. When MBA is high and CSA/W/RA enable a read, A0–A31 outputs Mail2 contents; when low, they output FIFO2 data. Similarly, MBB high selects Mail1 for B0–B31 output. This enables non-FIFO data exchange - e.g., configuration commands or status words - without consuming FIFO storage.

Can the SN74ACT3638-15PCB operate with CLKA and CLKB running at different frequencies?

Yes, the SN74ACT3638-15PCB explicitly supports asynchronous CLKA and CLKB operation - meaning they may run at different frequencies, phases, or duty cycles. All Port-A flags (IRA, ORA, AFA, AEA) are synchronized to CLKA, and all Port-B flags (IRB, ORB, AFB, AEB) to CLKB, using two-stage flip-flop chains to mitigate metastability. TI SCAS228D confirms this capability in the Functional Description and Synchronized FIFO Flags sections.

SN74ACT3638-15PCB Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: *

Package/Case:: -

Packaging:: Bulk

Product Status:: Active

Programmable:: Not Verified

Memory Size:: -

Function:: -

Data Rate:: -

Access Time:: -

Voltage - Supply:: -

Current - Supply (Max):: -

Bus Directional:: -

Expansion Type:: -

Programmable Flags Support:: -

Retransmit Capability:: -

FWFT Support:: -

Operating Temperature:: -

Mounting Type:: -

Supplier Device Package:: -

SN74ACT3638-15PCB FAQ

1.How can I place an order for SN74ACT3638-15PCB through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74ACT3638-15PCB on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

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The price and inventory of SN74ACT3638-15PCB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ACT3638-15PCB is usually 5 days.

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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 SN74ACT3638-15PCB?

For technical support, including SN74ACT3638-15PCB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ACT3638-15PCB requirements.

6.How does Aetrix verify that SN74ACT3638-15PCB is sourced from the original manufacturer or authorized distributors?

All SN74ACT3638-15PCB 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 SN74ACT3638-15PCB meets industry standards.

7.What is the process for return or replacement of SN74ACT3638-15PCB?

All SN74ACT3638-15PCB units undergo pre-shipment inspection (PSI). If there is an issue with SN74ACT3638-15PCB, 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 SN74ACT3638-15PCB part is unused and in its original packaging.

Return procedure for SN74ACT3638-15PCB:

1.Submit a request within 90 days.

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

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