TLF11963

June 1994

DP84902

17 EncoderDecoder Circuit

General Description

The DP84902 is designed to perform the encoding and de-

coding for disk memory systems It is designed to interface

directly with Integrated Read Channel Products (such as

National Semiconductor’s DP84910) and with Disk Data

Controller Products with a 2-bit NRZ interface (such as Na-

tional Semiconductor’s Advanced Disk Controllers) This

EncoderDecoder (ENDEC) circuit employs a 23 (17) Run

Length Limited (RLL) code type and supports the hard sec-

tored format

The DP84902 has the option of selecting either TTL or ECL

compatible code output to interface with preamplifiers com-

monly used in high data rate applications This is accomm-

plished by the setting of a bit in the control register

The ENDEC also includes write data precompensation con-

trol circuitry which detects the need for write precompensa-

tion This circuitry issues early and late output signals nec-

essary for precompensation The precompensation informa-

tion is generated against a 2T pattern The precompensa-

tion circuitry can be bypassed by the setting of a bit in the

control register

A control reigster is included to configure the ENDEC and to

select device operation options such as output code inver-

sion differential code output bypassing of the encoder and

the use of an internal write clock

The DP84902 is available in 20-pin SO and 20-pin SSO

packages

Features

Y

Operates at 2-bit Non-Return to Zero (NRZ) Data Rates

up to 50 Mbitssecond

Y

Y

Low Power Dissipation when TTL compatible code out-

put is selected 150 mW at 50 Mbitssecond NRZ Rate

Y

TTL Compatible Inputs and Outputs

Y

ECL Compatible Code Outputs (patented) are control

register selectable

Y

Two-bit NRZ Interface

Y

Supports Write Data Precompensation with Early and

Late output signals

Y

Selectable use of either an Internal or External Write

Clock

Y

Power Down Mode Included

Y

DC-Erasure is available to support Analog Flaw Map-

ping Testing

Y

Bypass Mode available which permits Un-Encoded Test

Patterns to be issued at the CODEOUT Pin

Block Diagram

TLF11963 – 1

FIGURE 1 DP84902 ENDEC Block Diagram

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