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NEe mlcrocomputers,lnc. /JPD371
Five Milita Drive/Lexington, Massachusetts 02173 Telephone (617) 862-6410 Telex 92--3434 TWX 710-326-6520
NEC MICROCOMPUTERS, INC.
MAGNETIC TAPE CASSETTE/CARTRIDGE
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
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
TABLE OF CONTENTS
INPUT/OUTPUT SIGNALS 7
PROCESSOR INTERFACE 7
TAPE DRIVE INTERFACE 14
ADDRESSABLE INTERNAL REGISTERS 17
WRITE REGISTERS 17
READ REGISTERS 27
TAPE CASSETTE/CARTRIDGE CONTROLLER EXAMPLES 32
PROCESSOR INTERFACE 32
TAPE DRIVE INTERFACE 35
Single Drive 35
Multiple Drive Systems 36
Other Formats 39
High Speed File Search 40
Parameters and Conventions 40
Listings of Drive Handling Routines 42
uPD37l SPECIFICATIONS 52
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
* ANSI = American National Standards Institute
1430 Broadway, New York, NY 10018
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.
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.
r-- - CASSETrEiCARTRIOOEcONTRoLLER --1 CASSETTE
I I DRIVE(S)
OR PROCESSOR I COMMANDS
MIN I COMPUTER DRIVERS AND
I I WRITE DATA
L ___________ (~
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