Service Request - Datron 1061A User Handbook Manual

Service request
A
wide variation
can occur
in
the
time taken
for
a
measurement
cycle,
dependant on
factors
such
as
the
magnitude of
the signal.
Therefore,
when
the
result
is
available, a service
request
(SRQ)
is
generated
by the
DVM
via the interface.
This
can
act as
a flag
(or interrupt) to a controller,
which
is
processing other data,
signalling that the
DVM
requires service.
Q1
and Q3 allow
an
SRQ
to
be generated
on
completion
of
any reading while
Q2 and Q4 allow
generation of
SRQ
only
when
a reading
is
'out
of
limits',
or
when
a
new
maximum
or
minimum
occurs.
Programming Q3
or
Q4
inhibits
further
triggers until
the
DVM
has been
serviced.
An
SRQ
will
always be generated
on power up and
when
a
syntax or option error occurs.
Q0
however,
will
supress other
SRQ's
normally generated.
Serial Poll
and
Status Byte
In a
system with various devices,
many
of
them
could request service
and
to
determine which of
Status byte
bB b7 b6 b5
b4 b3 b2 bl
l
t
j
i
Invalid
measurement
SRQ
Syntax
error
Option
error
Valid
measurement
(b8
=
0)
Normal
reading
0000
'Hi' limit
transgressed
XXXI
'Lo' limit
transgressed
XXIX
New maximum
X
1
X X
New minimum
I
1
X
X
X
x
=
I
or
0
Invalid
measurement
(b8
—
1)
Overload
/valid recall
Arithmetic overflow
Invalid
data entry/ invalid
recall
Error readout invalid
Input zero
or
calibration failure
DC
self test
failure
Ohms
self
test failure
AC
self test
failure
Current self test failure
Arithmetic
underflow
Binary
dump
available
Reference finished
(see
code
P2)
Self
test
finished
memory
fail
Self
test
finished
memory
pass
Power-up/
memory
fail
Power-up/memory
pass
these devices
had
initiated
a
request, either
a
serial
poll
or a
parallel poll
would
be undertaken by
the
controller.
During
a
serial
poll
each device
sends
its
status
byte
on
command,
and the controller
checks
the
request
bit,
thus
determining
a requesting
device.
The
DVM
has
many
reasons for
requesting service
and with
the additional
bits
available
in
the
status
byte
this
information
is
transferred
at
a serial poll.
Parallel poll
The
parallel poll
capability
provided
for
in
the
DVM
allows a controller
with
similar capability to
more
quickly
determine
which
device
is
requesting
service.
The
controller can, at
any
time,
conduct
a
parallel poll
when
all
devices,
which have been
configured to
respond, will
place
on separate bus
data lines
a positive poll
response
if
the
device
was
requesting service
or a negative poll
response
if
the
device
does not require
service.
With
eight
data
lines
available the controller
can
simultaneously
check
eight responses.
Having
determined the
requesting devices
from
the
parallel poll
the controller
would
normally conduct
a
serial poll
of these devices to
determine the
reason
for the request.
The configuration of a
device
to
respond
to
a
parallel poll consists of
determining
the
DIO
line
on
which
the
response
will
occur,
and
the
sense
(0
or
1)
of
the positive poll
response.
The negative
poll
response gives the
opposite
sense.
The
DVM
can
only
be configured for
this
response by the
controller.
The
configuration sequence
is
given
later
in this section.
The
DVM
must
be
serviced
by
either
reading
the
output or
by
reprogramming
to
allow the
generation of subsequent service requests.
To
aid
the user
in
servicing the
instrument
by
reading, a character string
is
always available for
output
on generation of
an
SRQ
even
if
a
measurement
is
not available.
This string in
O0
and
01 modes
is
"ICrLf'
and
in
02 and
03 modes
all
four
bytes contain
255
10
(all
1's).
These
'null'
strings
occur with syntax
or
option
programming
errors
if
no
measurement
is
available.
0000
000
1
00
10
00
1
I
0
1
00
0
10
1
0
110
0 111
1
000
1
00
1
10 10
10
11
1100
110
1
1110
1111
4-7