TLF9579

May 1991

DP8406 (54F74F632)

32-Bit Parallel Error Detection and Correction Circuit

General Description

The DP8406 device is a 32-bit parallel error detection and

correction circuit (EDAC) in a 52-pin or 68-pin package The

EDAC uses a modified Hamming code to generate a 7-bit

check word from a 32-bit data word This check word is

stored along with the data word during the memory write

cycle During the memory read cycle the 39-bit words from

memory are processed by the EDAC to determine if errors

have occurred in memory

Single-bit errors in the 32-bit data word are flagged and cor-

rected

Single-bit errors in the 7-bit check word are flagged and the

CPU sends the EDAC through the correction cycle even

though the 32-bit data word is not in error The correction

cycle will simply pass along the original 32-bit data word in

this case and produce error syndrome bits to pinpoint the

error-generating location

Dual-bit errors are flagged but not corrected These errors

may occur in any two bits of the 39-bit word from memory

(two errors in the 32-bit data word two errors in the 7-bit

check word or one error in each word) The gross-error

condition of all LOWs or all HIGHs from memory will be

detected Otherwise errors in three or more bits of the

39-bit word are beyond the capabilities of these devices to

detect

Read-modify-write (byte-control) operations can be per-

formed by using output latch enable LEDBO and the indi-

Diagnostics are performed on the EDACs by controls and

internal paths that allow the user to read the contents of the

Data Bit and Check Bit input latches These will determine if

the failure occurred in memory or in the EDAC

Features

Y

Detects and corrects single-bit errors

Y

Detects and flags dual-bit errors

Y

Built-in diagnostic capability

Y

Fast write and read cycle processing times

Y

Byte-write capability

Y

Guaranteed 4000V minimum ESD protection

Y

Fully

pin

and

function

compatible

with

TI’s

SN74ALS632A thru SN74ALS635 series

Simplified Functional Block

TLF9579 – 9

Device

Package

Byte-Write

Output

DP8406

52-Pin

yes

TRI-STATE

DP8406

68-Pin

yes

TRI-STATE

FAST

and TRI-STATE

are registered trademarks of National Semiconductor Corporation

C1995 National Semiconductor Corporation

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