Marconi Instruments 2955 - Page 75

OPERATION
!
Operating
example
Set
the
signal
generator
to
123,5
NIHz (with
increment/decrement
step
set to
iOO
kHz) at a level
of —30
dBm
modulated
by
i.O
kHz
a.m. at
50^,
preparatory
to measuring
signal
to noise
ratio.
The following
string
is
sent
after
addressing
the
instrument
as
a listener:-
RX:RG:FRi23.5M2;Dn0OKZ:LV-3ODM:SM:FRlKZ:LV50AM;MDI;AC:SN2<LF>
This
breaks
down
as foilows:-
RX
RG
FR123.5MZ
DIIOOKZ
LV-30DM
SM
FRIKZ
LV50AM
MDl
AC
SN2
Receiver
test
RFgenerator
Frequency
123.5
MHz
Delta
increment
lUOkHz
Level
-30
dBm
Set
modulation
Frequency
1 kHz
Level
a.m.
Modulation
on
AC
coupled
Signal/noise
When
ready
.
the
level
and
distortion
results
can
be selected
for reading
bv
sending
the following:—
RD6<LF>RD7<LF>
Then
the
instrument
is
addressed
as a
talker
to
receive
the result.
Trigger
The
bus
trigger
system
can
be used
to
start
the
transmission
of
a
tone burst whilst
the instrument
is
in
the
RX
mode.
However,
the
tone
sequence
must have
been previously set
up.
Typical
trigger
commands
include
Selective
Device
Trigger
( SDT) and
Group E.xecute Trigger
(GET).
Service
requests
(SRQ)
and
status
byte
When
enabled,
the
29::o can
request
service
to
indicate
to the
controller that
data is
ready
or to
warn
of
an error
condition.
In
response
to a
serial
poll after
asserting SRO. the
2955
provides
a
status
byte
whose
bits
are
allocated
as
shown
in
Fig.
3-
15.
Functions
asseneo
when
the
Pits are I’
or
true
Data ready
——
—
.Service
request
—
—
•
Error
has
occurred
Error bit
4—
N’umcncal
entry
—
Error bit
3—
Data
error
—
Error
bit
2
—
Abnormal
operation
—
Error bit
I—
.Syntax
error
—
—
Error
bit
0—
[nput'output
buffer overtlow
Notes...
(
1 )
DATA
READY
and
ERROR
bits
arc
cleared
after
the ne.xt time the
instrument
is
addressed
to
talk.
(
2)
The
SERVICE
REQUEST
bit
is
cleared
after
a
serial
poll.
46381 -622N
Apr.
83
3-51