Advertisement
Model 8901B
Service
8-7. SPECIAL FUNCTIONS
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 a thorough understanding of the instrument and the
service technician who needs arbitrary control of the instrument functions. During normal use, the
Modulation Analyzer safeguards itself against invalid measurements. Safeguards come in the form of
automatic tuning and ranging, overpower protection, squelch, modulation output blanking, and error
messages. When Special F'unctions are used, some of these safeguards are removed, and thus there is
a degree of risk that the measurement may be invalid. However, there
is no risk 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 finction 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, a special code, or, in some cases, the display is unaltered.
Special F'unctions can be entered from the
HP-IB
by issuing the Special h c t i o n 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
suffix. All software safeguards are relinquished.
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 Special finctions in the Detailed Operating Instructions in Section 3 and on the
Operating Information pull-out cards.
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.
1-39:
40-99:
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. A summary of the Direct Control Special Functions and codes is contained in Service Sheets A
and B.
Direct Control Special Function Code Forthat.
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 Principles
of Operation for Service Sheet BD5. Specific Direct Control Special Function codes
are
used in the
troubleshooting section of the individual service sheets.
As the Direct Control code is entered, the code will appear on the display. Pressing the SPCL key
initiates the Special F'unction. The display will then be in the form
OOrrrr.wwww,
where each digit
represents a binary bit
(0
or
1).
The
rrrr is
the
d
(data) read back from the Instrument Bus. The
wwww
is
the
d
(data) written to the bus. Thus
rrrr
and
wwww
are normally the binary form of the
Special Functions
8B-1
Advertisement
