Section 6: 9100 System Operation — SCPI Language
6-13
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6.4.3.2
9100 STATUS Subsystem
Input/Output Control transfers messages from the 9100 output queue to the system bus;
and conversely from the bus to either the input buffer, or other predetermined destinations
within the device interface. It receives the Status Byte from the status reporting system,
as well as the state of the Request Service bit which it imposes on bit 6 of the Status Byte
response. Bit 6 reflects the ‘Request Service state true’ condition of the interface.
6.4.3.3
Incoming Commands and Queries
The Input Buffer is a first in - first out queue, which has a maximum capacity of 128 bytes
(characters). Each incoming character in the I/O Control generates an interrupt to the
instrument processor which places it in the Input Buffer for examination by the Parser.
The characters are removed from the buffer and translated with appropriate levels of
syntax checking. If the rate of programming is too fast for the Parser or Execution
Control, the buffer will progressively fill up. When the buffer is full, the handshake is
held.
The Parser checks each incoming character and its message context for correct Standard-
defined generic syntax, and correct device-defined syntax. Offending syntax is reported
as a Command Error, by setting true bit 5 (CME) of the Standard-defined Event Status
register (refer to Sub-Section 6.5 ‘Retrieval of Device Status Information’).
Execution Control receives successfully parsed messages, and assesses whether they
can be executed, given the currently-programmed state of the 9100 functions and
facilities. If a message is not viable then an Execution Error is reported, by setting true
bit 4 (EXE) of the Standard-defined Event Status register. Viable messages are executed
in order, altering the 9100 functions, facilities etc. Execution does not ‘overlap’
commands; instead, the 9100 Execution Control processes all commands or coupled
groups of commands (see Note in left column) ‘sequentially’ (ie. waits for actions
resulting from the previous command to complete before executing the next).
6.4.3.4
9100 Functions and Facilities
The 9100 Functions and Facilities block contains all the device-specific functions and
features of the 9100, accepting Executable Message Elements from Execution Control
and performing the associated operations. It responds to any of the elements which are
valid Query Requests (both IEEE 488.2 Common Query Commands and 9100 Device-
specific Commands) by sending any required Response Data to the Response Formatter
(after carrying out the assigned internal operations).
Device-dependent errors are detected in this block. Bit 3 (DDE) of the Standard Event
Status register is set true when an internal operating fault is detected. Each reportable
error number is appended to the Error Queue as the error occurs.
Note: Coupled Commands
Coupled commands are best described by
an example:
In Section 7, on pages 7-5 and 7-10, the
'Volt-Hz' and 'Amp-Hz' profiles are given.
In the 9100, no AC output can be generated
whose product of amplitude and frequency
occurs outside the relevant profile.
With sequential execution of commands a
change in amplitude and frequency
(e.g.:VOLT 121;:FREQ 10E3 - a setting
within the profile) would cause an execution
error if the present frequency was 50kHz,
as the combination of 121V and 50kHz is
outside the profile
Such anomalies are overcome by defining
a coupling between commands which
allows the execution of the individual
components to be deferred until all
contiguous coupled commands in the same
group have been parsed and the validity of
the combination checked
Note that this does not require that all the
coupled components in a group must be
supplied for each new signal but that those
programmed will be correctly parsed.
Individual commands may be a member of
several coupled command groups. Refer to
Appendix A to this Section, page 6-A1, for
details of coupled groups.
