Tektronix 2221 - Page 85

Options and
Accessories
-
2221
Operators
п
П
.
Option 10
Status
and
Error
Reporting
4.
Enable the
service -
request
handler .
o
5. Get
the
command to
send
to
the
oscilloscope .
6.
Send
the
command
to
the
oscilloscope .
7.
Check for a
response
from the
oscilloscope .
The
status
and
error
reporting
system of
Option 10
interrupts the GPIB
bus
controller by
asserting
an
SRQ
( service request ) . The service request indicates that an
event has
occurred
that
requires
attention
. When
the
con
troller polls
the bus , the
status - byte
returned
by
the
oscil
loscope
indicates
the type of
event that
occurred
. A
further
EVEnt
?
query will
return an
event code
that
gives
more
specific
information
about the
cause of the
service
request . The
SRQ status byte
and the
event
code provide
a
limited
amount of
information
about the
specific
cause
of
the
service request .
Command
errors
,
execution
errors
,
and
internal errors
assert an
immediate SRQ ( if
RQS is
on ) . To
retrieve
other
system
event and
warning
status
bytes ,
OPC must
also be ON ,
and the
oscilloscope must
be queried by the STAtus ? command . See Tables 7-34
and
7-35
at the
back
of
this
section
for
status and
event
codes .
8. If
there
is
desired
function .
response , perform
the
O
9. You
are
ready for a
new
command .
Repeat
the
functions in
statements 5
through 9
as
many
times
as
desired
.
GPIB
Programming
Programming
considerations are
provided
in
this part to
assist
in
developing your own
unique
programs
for
inter
facing to the oscilloscope via the GPIB .
O
n
SERVICE
-
REQUEST
HANDLER_Typical
service
request
handler
routine
contains
the
necessary
instructions to
permit
proper processing of
interrupts .
For example , whenever power - on occurs , the oscillo
scope
asserts
an SRQ
interrupt
. If
a GPIB
program
is
operating on the controller when a power - on SRQ is
received , the program should be able to determine that
the oscilloscope's power was interrupted at some time
during program operation . This event could cause
improper program execution , unless the program was
written to
adequately
handle
the
possibility of a
power - on SRQ occurring .
Before a
program
can be
used for
controlling the
oscil
loscope , the
GPIB
parameters (
primary
address ,
message
terminator
,
and talk /
listen mode )
must be set .
Procedures
describing
how
these
parameters are selected
and set at
the
oscilloscope were given
previously
in this
section of
the
manual
.
Other interrupts ( or events ) for which the oscilloscope
asserts SRQ are identified in Table 7-14 .
Programs are usually
composed
of two
main parts
( or
routines ) ,
which can
be
generally
categorized as a
com
mand
handler and a
service
-
request
handler
.
While
some
controllers
have the
capability of
ignoring
service requests , others require that all SRQs be
managed . The programmer should understand the con
troiler being used . If service requests are to be handled in
the program , the interrupts must first be enabled .
П
COMMAND
HANDLER -
Basically , a
command
handler
should
establish
communication
between the
controller
and
oscilloscope
,
send commands
and
queries
to
the
oscilloscope ,
receive
responses from the
oscilloscope ,
and
display
responses as
required
. The
following out
line
indicates the
general
sequence of
functions
that
the
command -
handling
routine
should
perform to
accommodate
communications
between
the
controller
and oscilloscope over the GPIB .
A service -
request handler routine can
be
developed to
service
interrupts
when
they
occur
during
program
opera
tion . It
basically
should
consist of
an
interrupt
-
enabling
statement ( ON
SRQ )
near the
beginning of the
program
and a
serial
-
poll
subroutine
somewhere in the
program .
The ON
SRQ
statement
directs
program
control to the
serial
-
poll
subroutine
whenever an
SRQ
interrupt
occurs .
For
each interrupt
received by the
controller , the
program
should perform a serial - poll subroutine .
1.
Initialize the
controller .
2.
Disable
the
service -
request
handler
until
the
pro
gram
is
ready to
handle
them .
П
П
C
3.
Get
the
GPIB
address of
the
oscilloscope .
The following general steps are required to handle ser
vice
quests from
the
oscilloscope :
7-9