Topic       : Chips 'n Chips
Author      : Michael Ruge
Version     : chips_x.hyp (01/05/2001)
Subject     : Dokumentation/Hardware
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   INTRODUCTION

   To meet the demand for a low cost compact LSI Floppy Disk Control-
   ler device, Western Digital has developed the WD1772-02. The
   WD1772-02 is an NMOS Floppy Disk Controller device that incorpora-
   tes the FD179X, a digital data separator und write precompensation
   circuitry all in a single chip. The device offers soft sectors for-
   matting, selectable stepping rates, automatic track seek with ve-
   rify, and variable sector lengts. The WD1772-02 comes in a 28-pin
   dual-in-line or quad pack und operates from a single 5 Volt only
   power supply.


   APPLICATIONS

   The Mini-Floppy Controller is targeted for the low cost sector of
   the disk drive market, where digital data separation is preferred
   over analog phase lock loop
 Phase Locked Loop
 Insbesondere in der Nachrichtentechnik werden Oszillatoren 
 eingesetzt, deren Frequenz von einem äußeren Signal auf 
 die Referenzfrequenz synchronisiert werden kann. Hierdurch
 wird beispielsweise die Generierung von verschiedenen 
 Frequenzen ermöglicht. Das Kernstück eines PLL-Schalt-
 kreises besteht aus einen spannungsgesteuerten Oszillator
 (VCO - Voltage Controlled Oscillator oder auch Spannungs-
 Frequenz-Umsetzer), dessen Ausgangsfrequenz über eine 
 Spannung um seine Grundfrequenz nach oben bzw. unten ab-
 stimmbar ist.
. Included in this market are Personal
   Computers, Portable Computers und Small Business Computers.


   HOST INTERFACING

   Interfacing to a Host processor is accomplished through the eight
   bit bi-directional Data Access Lines (DAL) und associated control
   lines. The DAL is used to transfer data, status, and control words
   out of or into WD1772-02. The DAL having three states enabled as an
   output when Chip Select (CS) is active low and Read/Write (R/W) is
   high or as input receiver when CS und R/W is low. When transfer of
   data with the device is required by the Host CS is made low. The
   address bits A0 and A1 combined with the R/W line select the regi-
   ster und the direction of data.

   During Direct Memory Acces (DMA) data transfers between the
   WD1772-02 und Host Memory, the Data Request (DRQ) line is used in
   Data Transfer Control. This signal also appears as status bit 1 du-
   ring Read/Write operations. On Disk Read operations the DRQ is ac-
   tive when an assembled byte is present in the Data Register, then
   reset when read by the Host. If the Host fails to read the Data Re-
   gister before the following byte is assembled in the Data Register,
   the lost data bit is set in Status Register.

   At the completion of every command INTRQ is asserted. INTRQ is de-
   asserted by either reading the status or by loading the command
   Register.


   DISKETTE DRIVE INTERFACING

   The WD1772-02 has two modes of operation depending on the state of
   DDEN, regardless of the state DDEN the CLK input remains at 8Mhz.
   Disk Reads with sector lengths of 128, 256, 512 und 1024 byte sec-
   tor in both FM or MFM from diskettes is accomplished via the inter-
   nal digital data separator. Disk Write operation in MFM on inner
   tracks may require write precompensation. Write precompensation is
   enabled when bit 1 = 0, in the Write command and a precompensation
   value of 187 nsec is produced. The diskettes spindle motor is con-
   trolled by bit 3 of any Type I, II oder III command, upon receiving
   a command with bit 3 = 0, the spin up sequence is enabled.


     weiterblättern
     Kapitel Ein Kurzauszug aus der Dokumentation zum WD1772, Seite 1