Specifications
14
jumper onto
this
pair
of
pins. Another possible source of the
STROEE
pulses
is
through pin
12
of
P30.
If
this
is
used as
an
input.to.
the
A/D.
then the jumper
bet~een
Be
and
9C
~st
be
absent.
ThlS
lnput
is
not gated
and
will
always
respond to a
n~gative
transition.
P3D
may
be
used
in
its
normal
role as the multiplexer expansion connector
and
still
be
available
as
an
external strobe input
due
to the
ability
to daisychain ribbon
cables.
This
same
line
also
allows multiple
A0212
systems
to
initiate
convers;on~
synchronously.with
one
anot~er.
For
this
configuration,
all
P3D's. Pl"
12
must
be
t,ed
together wlth a
daisy-chained ribbon cable.
All
but
one
board
must
have
jumper
ac
to
9C
absent, the remaining board providing the
STROBE
s~urce.
The
simplest
way
to obtain the
maximum
conversion
rate
of
a
module
is
to
usej~mperarea
F.
This pption
is
enabled
by
jumoering
3F
to
4F,
4C
to
16C,
5C
to
17C,
removing
19C
to
20C
and
jumpering pins 2
and
3
(external strobe) together
on
P3
of
the mother board. This causes
the
A/D
~dule
to free-run; strobing
itself
at
its
own
maximum
rate.
This
rate
is
the reciprocal
of
the
sum
of
the conversion time
and
the
DLYOUT
signal
and
hence
can
be
adjusted to
some
extent
on
certain
modules
by
the knowledgable user
by
agjusting the
DLYOUT
signal. Bit
3 in the
command
register
now
serves
as
a run/stop control
9uch
that
a zero causes continuous conversions.
It
is
not necessary to
send
out
a strobe in software using the free-run
mode.
See
page
56
for further
programming
clarification.
The
free
run
mode
of
operation will also function in
an
overlapped
(pipeline)
manner
by
jumpering
IF
to
2F
instead
of
3F
to
4F.
In
addition
to
all
of
the
restrictions
applying to overlapped operation described
below,
an
idiosyncracy internal to the
AID
module
prevents
it
from
loading
or incrementing to a
new
channel while in the overlapped. free-run
mode.
The
desired channel
must
be
loaded while the
AID
module
is
stopped.
The
free-run feature
is
not available with the
MP6812
or
the
DT5703.
One
way
to increase the
module1s
throughput
is
to
advance
to a
new
input channel
and
allow
it
to
start
settling
before the current conversion
is
complete. This
is
known
as overlapped
or
pipelined operation. This
mode
of
operation
is
enabled
by
jumpering
AD
TRIG-
which
is
5C
or
16C
depending
on
the
module
to
17C
which
is
the
STROBE
pulse. This causes
the
STROBE
pulse
to
simultaneously
initiate
(rather
than sequentially
initiate)
an
A/D
conversion
and
the advance to the next channel. This
complicates the
acquisition
process because
two
strobe pulses are normally
required to
make
a measurement.
The
first
STROBE
pulse causes the multi-
plexer to point to the desired channel; the second
one
starts
the
AID
conversion for the channel
that
the
first
pulse caused the
MUX
to point
to.
The
second
pulse also simultaneously advances the
MUX
to the next
desired channel.
One
must
take care
when
writing the software
that
a
given data
word
is
associated with the
correct
channel
number
when
using
overlapped operation. Highest throughput
is
obtained
when
the strobe
period
is
slightly
longer than
either
the inputt amplifier
settling
time
or
the
AID
conversion time, whichever
is
greater.
This
mode
of
pperation
can
be
especially
fast
if
only
one
channel
is
being
measured
because
now
one
need
not wait for the input amplifier to
settle
due
to channel switching.
The
throughput
is
now
limited only
by
the
AID
conversion
time
if
the input
signal
is
not
above
the bandwidth
of
the input amplifier.
The
latter
could occur with
high
gain modules. Single channel,
high
gain
measurements
in
this
mode
may
provide
an
order
of
magnitude
or
more
increase in throughput.