6100B/6105A
Users Manual
5-10
5-17. Incoming Commands and Queries
The Input Buffer is a first in, first out queue, which has a maximum capacity of 1024 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 “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 instrument 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 instrument functions, facilities etc. Execution does not overlap commands; instead, the
Instrument Execution Control processes all commands sequentially (for example, waits for
actions resulting from the previous command to complete before executing the next).
5-18. Instrument Functions and Facilities
The Instrument Functions and Facilities block contains all the device-specific functions and
features of the instrument, 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 instrument 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.
5-19. Outgoing Responses
The Response Formatter derives its information from Response Data (being supplied by
the Functions and Facilities block) and valid Query Requests. From these it builds Response
Message Elements, which are placed as a Response Message into the Output Queue.
The Output Queue acts as a store for outgoing messages, until they are read over the
system bus by the application program. For as long as the output queue holds one or more
bytes, it reports the fact by setting true bit 4 (Message Available MAV) of the Status Byte
register. Bit 4 is set false when the output queue is empty. Refer to “Retrieval of Device
Status Information”.
5-20. Query Error
Query Error is an indication that the application program is following an inappropriate
message exchange protocol, resulting in the Interrupted, Unterminated or Deadlocked
condition: Refer to Bit 2 in “Event Status Register”.
The Standard document defines the instrument’s response, part of which is to set true bit 2
(QYE) of the Standard defined Event Status register.
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