Model
8903B
Service
8-20.
SPECIAL
FUNCTIONS
8-21.
General
Special Functions extend user control of the instrument beyond that normally available from the front panel.
They are intended for the user who has an understanding of the instrument and the service technician who
needs arbitrary control of the instrument fiinctions. During normal use, the Audio Analyzer safeguards itself
against invalid measurements. Safeguards come in the form of automatic tuning and ranging, overvoltage
protection, and error messages. When Special Functions are used, some of these safeguards are removed,
depending on the Special Function selected, and thus there is a degree of risk that the measurement may be
invalid. (However, there is
no
rish of damage
to
the instrument.)
To
enter a Special Function, enter the Special Function
code
(usually a prefix, decimal, and
suffix),
then press
the SPCL key. The Special Function code will appear on the display as it is being entered. If
a
mistake is made
during entry of the Special Function code, press the CLEAR key and start over. When a Special Function is
entered,
the
light in the SPCL
key
will usually go on (if it is not already on). The readout
on
the display will
depend
on
the Special Function entered. The readout may be a measured quantity, an instrument setting, or a
special code, or, in some cases, the display is unaltered. Special Functions can be entered
from
the HP-IB by
issuing the Special Function code followed by the code SP or sp.
The Special Functions are grouped by prefix range as follows:
0:
Direct Control Special Functions.
These functions are used for service. They halt the functioning of
the Controller and configure the instrument hardware as dictated by the suftix. All software safeguards
are relinquished.
1-39:
User Special Functions.
These functions are used during normal instrument operation when a special
configuration, measurement, or information
is
required. Many of the instrument safeguards remain
implemented. More information
on
User Special Functions can be found under
Spcciul
Fundions
in the
llc~/ailtd
Opcro/ing
Ins/riiclionI
in Section
3
and on the Operating Information pull-out cards.
SERIAL PREFIX 2742A AND
ABOVE:
Special Function
47
selects either 50 or
600
ohm Source Output
Impedance.
40-99: Service Special Functions.
These functions are used
to
assist in troubleshooting an instrument fault.
The functions available are quite diverse and include special internal measurements, software control,
and special service tests and configurations. Safeguards are generally relinquished.
8-22. Direct Control Special Functions (Prefix
0)
Communication between the instrument’s Controller and its hardware is via the Instrument
Bus.
During normal
instrument operation, the
instrument
Bus
carries measurement results, status information, and commands
(which control hardware). The Direct Control Special Functions halt the
bus
activity and send
out
commands
as determined by the code suffix. One command is sent for each Special Function entry.
Direct Control Special Function Code Format.
The Direct Control Special Function code is in the form
O.esd,
where
0
is the prefix (which may be omitted) and
esd
represents a three-digit hexadecimal number.
The significance of esd (which stands for enable, select, and data) is discussed in the
Priiiciplcs
o/
Opc’ralion
for Service Sheet BD4. Specific direct control codes are given in the
Troiihkcihoo/rng
section
of
the individual
service sheets.
As the Direct Control code
is
entered, the code will appear on the left display. Pressing the SPCL
key
initiates
the Special Function. The displays will then be
in
the
form
rrrr
(left display) and
wwww
(right display), where
each digit represents a binary bit
(1
or
0).
The
rrrr
is the
d
(data) read back from the Instrument
BLIS.
The
wwww
is
the d (data) written to the bus. Thus
rrrr
and
wwww
are normally the binary form
of
the hexadecimal
d. Exceptions to this are Special Functions 0.03d through
0.06d
and O.OBd through O.OFd, which control the
display itself.
Since the display has a limited set
of
segments for alphabetic characters, the hexadecimal characters A, B, C,
D,
E,
and
F
are displayed
on
entry as
-,
E,
H,
L,
P,
and blank respectively, and they are entered from the
keyboard
as
Shift
0,
Shift
1,
Shift
2,
etc., or from the
I-IP-IS
as
XO,
XI,
X2,
etc. Table
8-1
summarizes the
hexadecimal entry and readback
for
Direct Control Special Functions.
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