SN74ACT7811-25FN

FIFOs Memory Overview

The SN74ACT7811-25FN is a 1024-word by 18-bit synchronous first-in, first-out memory device from the Texas Instruments Widebus family. It operates within a supply voltage range of 4.5 V to 5.5 V and supports data rates up to 16.7 MHz with a maximum access time of 25 ns under a 50-pF load. The component features independent asynchronous inputs and outputs, allowing read and write operations to be synchronized to separate system clocks. It includes programmable almost-full/almost-empty flags and standard input-ready, output-ready, and half-full status indicators.

FIFOs Memory Feature Summary

• Supports synchronization of independent read and write operations to respective system clocks via dedicated enable circuitry.
• Features programmable almost-full/almost-empty flag boundaries defined during reset cycles or default values.
• Provides high-output drive capability suitable for direct bus interface applications.
• Allows expansion in both word width and word depth through cascading capabilities.

FIFOs Memory Applications

• High-speed data buffering between asynchronous clock domains
• Data storage in bit-parallel communication systems
• System interrupt handling and request processing

FIFOs Memory Procurement Notes

Verify the specific suffix FN indicates the 68-pin PLCC package configuration. Confirm the -25 speed grade corresponds to the required 25 ns maximum access time for your design timing constraints. Check current production status as this part may be obsolete or restricted. Ensure compatibility with existing 74ACT logic families if replacing older components.

FIFOs Memory Selection Notes

Select this component when designing systems requiring 18-bit wide data paths with deep buffering capabilities. The -25 speed grade is appropriate for applications operating at frequencies up to 16.7 MHz. Consider the 68-pin PLCC package constraints for PCB layout. Verify that the 4.5 V to 5.5 V supply range matches the target system power rails.

FIFOs Memory Part Context

This device belongs to the SN74ACT7811 series of clocked FIFO memories. It is pin-to-pin compatible with the SN74ACT7881, SN74ACT7882, and SN74ACT7884 variants, facilitating direct upgrades or replacements within designs utilizing those specific parts. The Widebus family designation indicates its optimized performance for wide data buses.

FIFOs Memory Replacement Considerations

Pin-to-pin compatible substitutes include SN74ACT7881, SN74ACT7882, and SN74ACT7884. Verify that alternative parts meet the specific 25 ns access time requirement and 18-bit data width specifications before implementation.

FIFOs Memory FAQ

How is the almost-full/almost-empty flag boundary programmed?

The boundary value (X) is programmed during the reset cycle. By holding the Define Almost Full (DAF) input low and pulsing RESET, the binary value present on data inputs D0–D8 is stored as the offset value X.

What is the function of the RDEN1 and RDEN2 inputs?

RDEN1 and RDEN2 are read enable inputs that must be high before the rising edge of the read clock (RDCLK) to allow data to be read out of memory. They do not affect the reading of the first word stored in the FIFO.