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PART
2.
REMOTE INTERFACE
21.3 DESCRIPTION
The
IEEE-488 bus and
RS-232 bus
on the
Remote
Interface
board provide remote
control of the
system.
The Remote Interface board provides
the
interface
for
the
IEEE-488 and
RS-232
buses,
thus
allowing
pro-
cessor control of
most
of the
functions normally
con-
trolled
from
the
front panel.
The
Remote Interface
board
also
contains a
multipurpose
input/output
(1/0)
port,
which can be used to
control equipment,
to
out-
put data,
or
to monitor data.
A
block
diagram
of
the Remote Interface
board
is
shown at the end of
the
section
in Figure 21-1,
a
sche-
matic
in
Figure 21
-5,
and
the printed wiring board
assembly
and
parts list in Figure
21-6.
Figure 21-4
shows
the
assembly and parts
list
of the
A17
RF Input
module's remote
option.
21.4 THEORY OF OPERATION
21
.4.1 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
buses,
which
are used for
reading
from
or writ-
ing 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 top
switch sets the least signifi-
cant
bit. Using the
binary
equivalent of the
address
number,
the operator can set the address. Setting the
switches
to
ON
gives
a logic 1.
21
.4.2
RS-232 BUS
INTERFACE
The
RS-232 bus
interface
circuit
provides
for
bus
buffering of the
interface protocol
as
defined by the
RS
-232
specification.
The system
processor
also
accesses this
interface directly
through
its
address,
data,
and control
lines.
The
programmer must
configure the
RS-232
com-
munication
parameters of the analyzer
to match
the
particular
controller that
is
being used.
This can
be
accomplished
by using
special function 95.
Once the
RS-232 port
parameters
are correctly set,
t he
pro-
grammer
need
only
connect the controller to the ana-
lyzer
using one
of
the
setups
described in
the
user
's
manual.
21
.4.3
RF-LEVEL CONTROL
The circuitry for RFwlevel control
selects
either the
5
VDC
+
AM MOD input for remote
control, or
the
AM
MOD
+
DC REF
(I)
input
for local
control.
For
21-2
remote
control,
t
he
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
potentiometer
controls the
RF
output
level.
For
the remote
control option, an electronically
pro-
grammable
RF
step attenuator is installed in
the
sys-
tem. The processor
controls the attenuator through the
address decode
and control
latch
circuitry
on the
Remote Interface board.
21 .4.4
MODULATION CONTROL
The Remote
Interface board
can
individually con-
trol
each of the three
modulation
sources.
For
remote
control, the
respective
modulation input
-
INT
MOD
(1),
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
(1),
and 1 kHz
SINE RTN
(I)
-
is selected and
sent
to the attenuator to control the modulation
level.
21 .4.5 ADDRESS-DECODE AND
CONTROL-
LATCH CIRCUITRY
With the address decode
and control latch circuitry,
the system
processor
has direct control over the
pro-
grammable 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 .4.6
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 1/0 ports
can be
configured
as either inputs or
outputs.
Data
is
written to or read from these ports via
the
remote bus.
All
t
hese
ports meet TIL
logic
level
requirements
for positive
logic. As
inputs, I/0 1 to 1/0
8
represent
no
more
than two
standard
TTL loads
each, while
1/0
9
to
1/0 16
are
high impedance loads.
As
outputs, each port can drive as many
as
two
stan-
dard
TTL
loads.
1/0 0
to
1/0 16
can
also
supply a
min-
imum
of 1
rnA
at
1.5
V de.
Two
pairs
of
ports are
connected to
relays
in
such
a
way
that
the two ports
of
each
set
are normally uncon-
nected.
H
owever,
when the
relay
is
activated, t he ports
are
shorted
together. Each relay port
can switch a
maximum of 28 V de
at 0.8
A. Each relay port
is also
isolated from the
system
chassis to
a voltage
level
of
500
Vdc.
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