June 1994
DP84902
1,7 Encoder/Decoder 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
Encoder/Decoder (ENDEC) circuit employs a 2/3 (1,7) Run
Length Limited (RLL) code type and supports the hard sec-
tored format.
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 Mbits/second
Y
a
Single 5V Power Supply Operation
Y
Low Power Dissipation when TTL compatible code out-
put is selected. 150 mW at 50 Mbits/second NRZ Rate
TTL Compatible Inputs and Outputs
ECL Compatible Code Outputs (patented) are control
register selectable
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.
Y
Y
Y
Y
Two-bit NRZ Interface
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.
Supports Write Data Precompensation with Early and
Late output signals
Y
Selectable use of either an Internal or External Write
Clock
Y
Y
Power Down Mode Included
DC-Erasure is available to support Analog Flaw Map-
ping Testing
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.
Y
Bypass Mode available which permits Un-Encoded Test
Patterns to be issued at the CODEOUT Pin
Block Diagram
TL/F/11963–1
FIGURE 1. DP84902 ENDEC Block Diagram
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
IBMÉ is a registered trademark of International Business Machines Corporation.
C
1995 National Semiconductor Corporation
TL/F/11963
RRD-B30M105/Printed in U. S. A.