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SECTION 21.
IEEE INTERFACE OPTION
REMOTE INTERFACE OPTION
PART
1.
IEEE
INTERFACE
21 .1 DESCRIPTION
An IEEE-488
bus
and
the
IEEE Interface board
provide
remote
control of
the
system.
The IEEE
Interface board provides the interface for the 488
bus,
thus allowing
processor-control
of
most
of the
func-
tions normally
controlled
from the
front panel. The
IEEE
Interface
board
also
contains
a
multipurpose
input/output
(1/0
) port,
which
can
be used to
control
equipment, to output
data,
or
to monitor data.
A
block
diagram
of
the IEEE
Interface
board
is
shown
at the
end
of
the section in Figure 21-1, a
sche-
matic
in
Figure 21-2,
and the
printed
wiring board
assembly and
parts
list in
Figure
21-3.
Figure
21-4
shows the assembly
and
parts
list of the A17
RF
Input
module's
IEEE
option.
21 .2 THEORY
OF
OPERATION
21.2.1
IEEE BUS INTERFACE
The IEEE
bus
interface
circuit
provides
for
bus
buffering
and
interface
protocol
as
defined
by
the
IEEE-488 specification.
The
system
processor
accesses
the
interface directly through its address,
data,
and
control
busses,
which are
used for
reading
from or
writing to the
IEEE
bus.
The
address
of
the
System
Analyzer's
IEEE
bus is
set
on
the
IEEE
Interface
board via the top four
switches
on
a
dip
switch.
The
least
significant bit
is
the
top switch. Using
the
binary
equivalent
of
the
address
number,
the
operator can
set the address. Setting
the
switches to ON gives
a logic 1.
21 .2.2
RF-LEVEL CONTROL
The
circuitry
for
RF -level control
selects
either
the
5 VDC
+
AM MOD
input for
remote
control or
the
AM
MOD
+
DC
REF
(I)
input for
local
control.
For
remote
control,
the
5 VDC
+
AM
MOD
input
is elec-
tronically
attenuated
to provide the
requested
RF
output level.
For
local
control, the attenuator is pro-
grammed
for
unity
gain so that the
AM
MOD
+
DC
REF
(I)
signal
from the front
panel's~RF-level
poten-
tiometer
controls
the
RF
output
level.
For the
IEEE
control option,
an electronically pro-
grammable
RF
step
attenuator
is
installed in
the
sys-
tem. The processor then
controls
the
at tenuat
or
21-1
through
the address-decode and control-latch circui-
try
on t
he IEEE
Interface
board.
21.2.3
MODULATION CONTROL
The
IEEE
Interface board can
ind
ividually
control
each
of
the
three modulation sources.
For remote
con-
trol,
the
respective
modulation
input-
INT MOD
(I),
EXT
MOD
(I),
and
1 KHz
SINE
(I)
-
is
switched to
a
programmable
attenuator.
The
system processor
selects
the
level
of
attenuation
necessary to provide the
requested level
of
modulation.
For local
control,
the
attenuators
are programmed
for
unity
gain, and
the
respective
modulation
signal from
the front
panel's
level
control - INT
MOD RTN
(1),
EXT
MOD
RTN
(I)
and
1 KHz
SINE
RTN
(l)
- is
selected and
sent
to
the
attenuator
to cont rol the
modulation
level.
21.2.4 ADDRESS-DECODE AND
CONTROL-LATCH CIRCUITRY
With the
address-decode and
control-latch
circui-
try, the system
processor has direct
control over
the
programmable attenuators
on the
board.
Control
data
on the
data
bus
(DO-D7)
is
latched
at the control
latch
indicated by the address bus (AO-A15).
21.2.5
MULTIPURPOSE
INPUT/OUTPUT AND
RELAY PORTS
A
side-panel
connector provides
16
multipurpose
input/output (I/0) ports and two pairs of relay ports.
The
I/0 ports
can be configured as either
inputs
or
outputs.
Data
is written to
or
read from these ports
via
the
IEEE
bus. All
these ports
meet
TTL
logic-level
requirements
for
positive
logic. As
inputs,
I/
0 1
to
I/0
8
represent
no
more
than
two standard
TTL
loads
each,
while
I/0 9 to 1/0
16
are
high-impedance
loads.
As outputs,
each
port can
drive
up
to
two
standard
TTL
loads. 1/0
9
to 1/0 16
can
also supply a
minimum
of
1
rnA
at
1.5V.
Two
pairs
of
ports
are connected
to relays
in
such
a
way that the two ports of each
set
are
normally uncon-
nected. However, when
the relay
is activated, the
ports
are
shorted
together.
Each
relay
port can
switch
a
maximum
of
28
Vdc at 0.8A.
Each relay
port
is
also
isolated from
the system chassis to
a voltage
level
of
500 Vdc.
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