Specifications
The input circuit lines have the following electrical specifications.
See
figure 2-2 for the
recommended
circuit.
True
= Logical zero =
Vin
±
0.0
to +
0.4
V @
lin
=
40
rnA (max)
False
= Logical
one
= Vin ±
2.5
to +
5.25
V @
lin
=
250
f-tA
(open)
Input Impedance
=
220/330
ohms
MAX 10 FEET I
RIBBON OR
20
FEET TWISTED
PAIR
+5V
7414
39216·10
FIGURE 2·2. INTERFACE
SIGNAL
DRIVER/RECEIVER
2.2.2
Input
Line
Termination
The
SA810/860
has been provided with a removable resistor pack for terminating the eight input lines.
In
order
for the drive to function properly, the last drive
on
the interface must have these eight lines terminated.
Termination of these lines can be accomplished
by
either of two methods:
a. As shipped from the factory, the resistor pack
is
installed in location U9. These packs
can
be
removed
from
all
drives except the last
one
on the interface.
b. External termination may be used provided the terminator
is
beyond the last drive. Each of
the
lines should be terminated
by
using a
220/330
ohm, 1/4 watt resistor, pulled
up
to
+ 5 V dc.
The
same
removable resistor pack
is
also prOVided for terminating the optional input lines.
2.2.3
Drive
Select
1·4
DRIVE SELECT, when activated
to
a logical zero level, enables
the
multiplexed I/O lines, starts
the
spindle motor,
energizes the
stepper
motor, locks the door,
and
lights the activity LED.
In
this
mode
of operation, only the drive
with this line active
will
respond
to
the input lines
and
gate the output lines.
Four separate input lines, DRIVE SELECT 1, DRIVE SELECT 2, DRIVE SELECT
3,
and
DRIVE SELECT 4, are
prOVided so that up to four drives may be multiplexed together
in
a system
and
have separate DRIVE SELECT
lines. Traces DS1, DS2, DS3,
and
DS4
have been prOVided to select which DRIVE SELECT line
will
activate the
interface signals for a unique drive. As shipped from the factory, a shorting plug
is
installed
on
DSl.
To
select
another
DRIVE SELECT line, this plug should be moved to the appropriate OS pin.
2.2.4
Side
Select
(SA860
Only)
This interface line defines which side of a two-sided diskette
is
used for reading
or
writing. An
open
circuit, or logical
one,
selects the
read/write
head
on
the
side 0 surface of the diskette. A short to ground, or logical zero, selects the
read/write
head
on
the side 1 surface of the diskette. When switching from
one
head
to the other, a
100
f-tS
delay
is
required before any read or write operation
can
be initiated.
Two optional methods of side selection are available
and
can be implemented by
the
user through appropriate
jumper connections. These options are described
in
paragraphs
7.5
and
7.6.
2-3