4-11-4. Response Header
The <Response Header> is available for use by the
device designer for device-specific responses. It may
be used, for example, to create responses in directly
resendable <Program Message Unit> format or to
identify response data to the controller. There are
three defined <Response Header> elements: <Simple
Response Header>, <Compound Response Header>,
and <Common Response Header. A <Simple Re-
sponse Header> is defined as:
<Response Mnemonic>
For example, FRQ. Leading <White Space> ele-
ments are not permitted. Upper/lower case alpha
characters are treated with the same semantic equiva-
lence. <Compound Response Header> is not used
in model 8020 and will not be discussed here. A
<Common Response Header> is defined as:
*<Response Mnemonic>
For example, *SRE. Leading <White Space> ele-
ments are not permitted. Upper/ lower case alpha
characters are treated with the same semantic equiva-
lence.
4-11-5. Response Data
A <Response Data> functional element is used to
convey a variety of response information related to
the <Response Header>. The element type is de-
termined by the eliciting query. <Non-Decimal Re-
sponse Data>, <String Response Data>, and <Arbi-
trary Block Response Data> functional elements are
not implemented in Model 8020. Therefore it shall
not be discussed in this manual.
4-11-5-1. Character Response Data
The <Character Response Data> functional element
is used to convey information best expressed
mnemonically as a short alpha or alphanumeric string.
It is useful when numeric parameters are inappro-
priate, for example, model number and manufacturer
identification.
4-11-5-2. Decimal Numeric Response Data
The <Decimal Numeric Response Data> is a flexible
version of the three numeric representations as de-
fined in ANSI X3.42-1975 - NR1, NR2, and NR3.
A <Decimal Numeric Response Data> elements are
defined as:
1. NR1 elements consists of a set of implicit
point representations of numeric values. i.e. (+/-
)12345.
2. NR2 elements are the representations of explicit
point numeric values. i.e. (+/-)12.345.
3. NR3 elements are representations of scaled
explicit radix point numeric values together with an
exponent notation. i.e. (+/-)123.456E(+/-)3.
4-12. READING FROM THE MODEL 8020
The reading sequence is used to obtain, from Model
8020, various <Response Message Units> such as
frequency, amplitude, offset or operating modes. The
<Response Message Unit> elements are placed in
an output queue. The output queue may be read
by device-defined queries. Such device-defined que-
ries cause the item read to be removed from the
output queue. Model 8020 executes the <Program
Message> elements in the order received. The output
is cleared when any of the following occur:
1. Reading all the items in the output queue.
2. Upon receipt of a new <Program Message>.
3. Upon receipt of the *CLS, DCL or SDC com-
mands.
4. Upon Power on.
IEEE-488.2 specifies that a device cannot send
<Response Message> elements unless commanded
to do so. This is specified as an “Unterminated
Action”. The “Unterminated Action” is executed when
the controller attempts to read a <Response Mes-
sage> from the device without first having sent a
complete Query Message, including the <Program
Message Terminator>, to the device. In the event
of “Unterminated Action” model 8020 performs the
following steps:
1. Sets the Query Error bit in the Standard Event
Status Register.
2. Clears the output queue.
3. Sets brq False.
If a read sequence is interrupted by a new <Program
Message> before it finishes sending a <Response
Message>, model 8020 executes an “Interrupted
Action”. GPIB bus response is similar to the “Un-
terminated Action”.
The reading sequence is conducted as follows:
1. The controller sets the ATN line true.
2. The Model 8020 is addressed to talk.
3. The controller sets ATN false.
IEEE-488.2 Operation Model 8020
Page 4-20
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