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uPD371_Magnetic_Tape_Controller_Jun77


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NEe mlcrocomputers,lnc.                                                                            /JPD371




                 MAGNETIC TAPE
         CASSETTE/CARTRIDGE CONTROLLER
                                          USERS' MANUAL




Five Milita Drive/Lexington, Massachusetts 02173   Telephone (617) 862-6410   Telex 92--3434 TWX 710-326-6520
   NEC MICROCOMPUTERS, INC.

             uPD371

MAGNETIC TAPE CASSETTE/CARTRIDGE

          USERS' MANUAL




                                   June 9, 1977
     The NEC uPD37l is a high performance N-Channel LSI tape
cassette/cartridge controller designed to interface between most
cassette or cartridge tape drives and most microprocessors or
minicomputers.

FEATURES - Compatible with ANSI, ECMA and ISO standards
         - Also compatible with most other standards
         - Hardware CRC generation and verification
         - Read after write capability
         - High speed file search
         - Multiple drive capability
         - May read or write on one drive while rewinding
           or file searching on another
         - Maximum Data Transfer rate of 375K bits/sec
           equivalent to 468 IPS at 800 BPI




                           2
                TABLE OF CONTENTS

INTRODUCTION                                     4

INPUT/OUTPUT SIGNALS                             7

     INTRODUCTION                                7

     PROCESSOR INTERFACE                         7

     TAPE DRIVE INTERFACE                       14

ADDRESSABLE INTERNAL REGISTERS                  17

     INTRODUCTION                               17

     WRITE REGISTERS                            17
     READ REGISTERS                             27
TAPE CASSETTE/CARTRIDGE CONTROLLER EXAMPLES     32
     PROCESSOR INTERFACE                        32
     TIMING                                     32
     TAPE DRIVE INTERFACE                       35

          Single Drive                          35

          Multiple Drive Systems                36
     SOFTWARE                                   39
          Introduction                          39
          Other Formats                         39
          High Speed File Search                40

          Parameters and Conventions            40

          Listings of Drive Handling Routines   42

uPD37l SPECIFICATIONS                           52




                         3
                         INTRODUCTION


     The uPD371 uses the ANSI, ECMA and 180* standard recording
technique of "bi-phase-level encoding". The name is usually
shortened to "phase encoding".

     In phase encoding a logic one is encoded as a positive
transition. A logic zero is encoded as a negative transition.
These data transitions are made to occur at intervals with a
constant period. Halfway between data transitions, a "phase"
transition may be required to establish the proper polarity for
the succeeding data transition. An example of phase encoded data
is shown in Line 1 of Figure 4.
     Data is usually recorded on magnetic tape in blocks called
"records". Records are separated from each other by regions of
erased tape called "inter record gaps" or just "gaps". The
lengths of both records and gaps depend on the recording standard
used. The uPD371 can adapt to any record or gap length.

     ANSI, ECMA and ISO records are made up of 8-bit bytes in
which the least significant bit is recorded first: The first
byte of a record (the "preamble") is an AA hex. The preamble is
followed by 1-256 "data" bytes. The data bytes are followed by
two "CRC" (Cyclic Redundancy Character) bytes. The CRC bytes are
followed by the l'ast byte of the record (the "postamb1e") which
is also an AA hex. The postamb1e is followed by an inter record
gap.  The uPD371 can write records which are completely
compatible with the ANSI, ECMA and ISO standard, but it is not
limited to this standard. See Other Formats in the SOFTWARE
section.




*   ANSI = American National Standards Institute
           1430 Broadway, New York, NY 10018
           USA
           Document Number ANSI X3.48-l977
    ECMA   =   European Computer Manufacturers' Association
               114 Rue du Rhone
               CH 1204 Geneva, Switzerland
               Document Number ECMA 34

     ISO   =   International Organization for Standardization
               c/o American National Standards Institute
               Document Number ISO 3407-1976

    All three documents are identical except for some minor
    differences in describing physical dimension tolerances.



                                4
     Most tape drive manuals contain amplified discussions of
encoding techniques and recording formats. The interested reader
is referred to these sources for further information.
      Figure 1 shows a uPD37l based tape controller in block
diagram form. The workload of operating the tape drive (or tape
drives) is shared between the uPD37l hardware and the processor
software. The uPD37l hardware encodes and decodes data for the
processor program, calculates the CRC during write operations,
verifies the CRC during read operations, informs the processor
program when to send data bytes during write operation and when
to read bytes during read operations, converts tape drive status
signals into register bit levels which may be read by the
processor program and converts software commands into signals
which may be understood by the tape drive(s).
      The software responsibility is usually divided between two
 sets of programs -- the Drive Handling Routines and the Operating
 System. The Drive Handling Routines must transfer read or write
 data when requested to do so by the uPD37l, monitor drive
 performance and issue tape motion commands. The Operating System
 determines the areas of memory from which write data is taken and
~into which read data is stored and what use is made of the data.

     A discussion of Cassette/Cartridge Operating Systems is
beyond the scope of this manual. Drive Handling Routines are
described in the SOFTWARE section. Complete listings are
included for a uPD8080A microprocessor as an example of typical
Drive Handling Routines. The uPD37l hardware is described in the
INPUT/OUTPUT SIGNALS and ADDRESSABLE INTERNAL REGISTERS sections.
Schematics and discussions of typical controllers are given in
the TAPE CASSETTE/CARTRIDGE CONTROLLER EXAMPLES section.




                            5
                             r-- -    CASSETrEiCARTRIOOEcONTRoLLER      --1      CASSETTE
                                                                                    OR
                                                                                 CARTRIDGE
                             I                                               I    DRIVE(S)
                             I                                               I
                             I                                               I
                             I                                               I
                             ~
                                                             -
    MICROPROCESSOR
            OR                    PROCESSOR                                  I    COMMANDS
                                  INTERFACE ~
     MIN I COMPUTER                                                DRIVERS           AND
                             I                                               I   WRITE DATA
                             I
                             I                      uPD371
                                                                             I
                                                                             I
 CASSETTE
                             I                                               I
    OR
CARTRIDGE
OPERATING
  SYSTEM
                DRIVE
              HANDLING
              ROUTINES
                             I
                             I
                             I
                                   TIMING
                                                -                            I
                                                                             .
                                                                             I
                                                                                  STATUS
                                                                                    AND
                                                                                 READ DATA


                             I                                               I
                             I                                               I
                                                                             I
                                                                             I
                             L ___________ (~



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