Operation
Strings
A string is the smallest complete message that can be sent
over the bus.
e.g.
"HSA=5E+3"
Commas may be used as separators within a string and
semi-colons can
be
used
to
separate strings from each other.
e.g.
"HSA=5E+3;ST1=1,2,3
.....
"
A string may contain only ASCII characters, except binary
blocks (see later).
The
space, character codes above 127
(decimal) and control codes
other
than line feed will be
ignored.
Numbers
Numbers that
appear
in commands must conform
to
certain
conditicns:
1.
2.
3.
4.
the number must contain less than
20 characters;
the mantissa must
be
an
integer, i.e. it must not con-
tain a decimal point; unless it
is
in the form 0.5E-3;
the
mantissa may contain a sign
(+/-);
+ will
be
assumed if none
is
specified;
the exponent
is
optional; if included it must
be
pre-
ceeded by
an
'E';
5. the exponent may contain a sign; if omitted +
is
assumed
Blocks
The
buffer of the 4070 is
of
limited size: when large data
transfers are being carried
out
it
is
necessary
to
break
them
into smaller groups,
or
blocks. Differences arise here bet-
ween
RS423 and GPIB working. RS423 accepts
<Cr>
and
<If>
as terminators in different combinations.
The
GPIB
port
does the same,
but
in addition, the dedicated
EOI
(End
Or
Identify) bus line may
be
used. This line can be asserted
with
the
final character
of
a transfer to signify
end
of
trans-
mission (as opposed
to
end
of
block). In
the
4070 this is
optional, the command
EOI
being used to enable
or
disable
the use
of
this line. Block termination codes available for
both ports are as follows (reference to
EOI
clearly relate
only to
GPIB working):
As separator between blocks:
1.
<Cr>
<If>
2.
<if>
without
EOI
asserted.
As final block terminator:
3.
<Cr>
<if>,
EOI
asserted with
<If>.
4.
<If>
with
EOI
(if
EOI
=ON
has been set).
5.
<If>
without
EOI
(if
EOI
=OFF
has been set).
Records
A record
is
a group of
one
or
more command strings.
The
strings will be separated by semi-colons within the record.
Records are separated in the same way as blocks
and
there-
fore the final record must be terminated by methods 3, 4
or
5 above.
Section 1
The
simplest form
of
record has a single string and
is
termi-
nated by a
<If>
with
EOI.
e.g.
"HSA=5E-3
<If>"
EOI
asserted with
<If>
If
a record
(or
a block) exceeds 82 characters, the command
interpreter will process the record as far as it can.
Each
complete command string within the 82 character
group will
be
executed, though an
error
message may
be
returned if
part
of a further command string occurs at
the
end
of
the buffer. This command will however be correctly
executed once it has been received complete.
Command Types
There
are three types of command:
Interrogative This
is
a request for information about instru-
ment status
or
for
the
contents
of
a memory to
be
tran:.mitted.
Assertive These commands request a change in
one
of
the
settings
or
memory
of
the instrument. They are only
valid when in
Remote
or
Local Lock
Out
mode. They
have
the
form
'parameter=
setting'.
Direct Action Assertive These commands have a direct
action
rather
than changing a setting. They are only
valid in
Remote
and
Local Lock
Out
modes.
Service Requests
Service requests are generated by
the
4070
to
inform the bus
controller that some event
or
problem has occurred. These
have no effect upon the instrument and may be ignored. In
response
to
a serial poll
or
the
SRQV command the 4070
will supply a number. This has the meaning given in Table
1.8.1.
Table
1.8.1
Service Requests
SRQNo.
0
74
81
96
98
99
100
101
102
103
104
105
Meaning
Ok
Completed
ETS Acquiring
Invalid command
SRO
stack overflow
Command buffer overflow
Selection failure
Not allowed when Local
Syntax
error
(parameter field)
Number
out
of
range
Length
error
(bulk transmissions)
Checksum
error
Sending and Receiving Stores
There are a few points to note when transferring data from
the display trace stores and the reference memory stores.
The
data may exceed the host computers' buffer size, and
may also require a considerable amount of time to transfer
(particularly using RS423 at a low baud rate).
23
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