Operational Characteristics
The following paragraphs describe the operational
characteristics
of
the CartriFile
40
tape unit: signal
levels, tape motion, data transfer rate and storage capacity,
and so forth.
INPUT/OUTPUT SIGNAL LEVELS
CartriFile
40
input
and output circuitry uses
Transistor-Transistor Logic (TTL), +2.5 to +5.0 v for
High
and
-0.5
to
+0.5 v for Low. Sink current requirements
for a Low input
will
not exceed 2 rna. The outputs can
supply 1 rna
at
minimum
High
voltage and can sink
10
ma
at
maximum Low voltage.
TAPE MOTION
The tape
is
driven at 10 inches per second in a
"forward"
direction in the three operating modes: Write Tape, Read
Tape, and Load-Point Search. "Reverse" or "backspace"
tape movement
is
not
possible.
RECORDING TECHNIQUE
The CartriFile
40
tape unit employs a bit-serial
phase-encoded, two-track recording technique with
record-error detection.
RECORD FORMAT
Records of sequential data words are written on the tape,
with the records separated by
gaps.
Each record may
contain any number of words,
as
determined by the
external control unit during writing.
The data words may contain 8, 12, or 16 bits. Either
8 or
12
bits-per-word formats may
be
program-selected
by the external control unit
or
fixed by wiring the select
input
to
ground
at
the interface. For 16 bpw,
no
ground
connection
is
required.
DATA TRANSFER
The data words are transferred in and out bit-parallel.
The data are written on the tapes bit-serial, with internal
circuitry making the parallel-to-serial conversion during
Writing and the serial-to-parallel conversion during Reading.
The using external control unit (e.g., digital computer)
has wide latitude in servicing the data transfers during
both
Writing and Reading. During Writing, a Write Data
Clock pulse
output
occurs
at
a fixed rate; the using control
unit has the major portion
of
the period between each
Data Clock
to
input
the data word with a Write Data
Transfer
input
pulse. During Reading, the data outputs
may be sampled by the external control unit at any time
1-4
during the major portion
of
the period between Read
Clock pulse outputs. Precise timing for the data transfers
is
given in Section III, OPERATION.
INTER-RECORD
GAPS
In Writing each record, a Write Start delay
of
16 msec
and a Write Stop delay
of
8 msec accommodate the
start-
and stop-tape motion transients and provide the
time for writing a 0.16-inch (maximum length) inter-record
gap. Internal circuitry times both delays and controls the
tape motion and gap writing.
After reading each record, internal circuitry recognizes
the inter-record
gap
remaining
to
accommodate the start
transient prior to reading the next record. The Read
Start and Read Stop delays are 9.5 msec and 4.75 msec,
respectively.
BEGINNING-OF-TAPE AND END-OF-TAPE
A 3-inch long photoreflective Load Point marker affixed
to the continuous-loop tape marks both the beginning
and the end
of
the tape. Each tape passes a photosensor
before reaching the magnetic head; the 1.45-inch separation
between the photosensorand head provides for the following
beginning-of-tape timing and end-of-tape warning.
On
writing the first record on a tape, a Write Start delay
of 375 msec
is
initiated after the Load Point marker passes
the photosensor
to
assure adequate beginning-of-tape
gap. The resulting total Write Start or Read Start delay
for the first record
is
therefore between 375 and 675
msec, depending upon the exact Load Point position
of
the tape when the Start Command
input
occurs.
An
end-of-tape warning
is
provided during Writing when
the leading edge of-the marker passes under the photosensor
and causes the Load Point status line for the tape to
go
True.
When
this occurs, 1.2 inches of the tape (up to
180
8-bit
words) may be written before a Write Stop
Command
is
mandatory.
DATA TRANSFER RATE
The bit rate
is
18,000 bits per second, recording 900
bits
to
the inch (at
10
inches per second) on two tracks.
The written tape format
is
bit-serial, and a Start bit
is
added to each half-word prior
to
writing
it
on
the tape.
The transfer rate during either writing or reading
is
therefore:
18,000
Transfer Rate =
B+2
words per second,
where B
is
the number
of
data bits in each word
at
the
data input and data
output
(Table 1-2).
