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Operation
and Programming
REPLACE BATTERY* SIGNAL
AND
LED
The
7706
has
onboard
circuitry
to
monitor
the battery
voltage.
It
indicates
when
the battery
life is
down
to
approxi-
mately two weeks.
It
does
this
in
two
ways:
When
Vcc
is
on,
an
LED
at
the
front
edge
of
the
card
turns
on,
and
the
Replace
Battery*
signal
activates.
This signal
is
accessible
at
a two-
pin
connector
on
the
front
edge
of
the card.
The
location
of
the
LED
and
connector
is
shown
in
Fig. 2-2.
Figure 2-4
shows
how
the signal
can be
connected.
It
can be
input
through
an input
port, in
which
case the processor
will
have
to
scan
the input
from
time
to
time,
or
it
can be
connected
to
an
inter-
rupt input.
If
an
input port
is
used,
any
spare
input line
in
the
system
can be
used. Pro-Log's
7804 Z80A
processor card
has
an
input
line
onboard which can be
used.
If
an
interrupt
inputisused, a
priority
interrupt controller
can
be
used,
such
as Pro-
Log's
7320
card,
or
an
interrupt input
on
the
processor
card
can be
used.
Pro- Log's
7801
processor card has
inter-
rupt
inputs available
on
the card. Instructions
for
replacing
the battery
are given
in
Section 5
of
this
manual.
MEMEX
MEMEX
is
an
STD
BUS
signal.
It
is
usually controlled
by
a
memory
segment
controller
or
an
output
port.
Most
Pro-Log
processor cards
have
the
ability to
control
MEMEX.
Its
func-
tion
is
to
allow
two banks
ol
memory, up
to
64K
each,
to
reside
in
one
system.
One
bank
is
enabled
when
MKMFX
in
high,
and
the
other
when
it
is
low.
It
is
useful
for
expanding
mem-
ory
beyond
64K,
and
in
bootstrapping.
In
bootstrapping, the
MEMEX
line
is
used
to
enable
the bootstrap
PROM
at
power-
up and
switch
to
a
block
of
RAM
after
bootstrapping
is
completed.
Figure 3-5
shows an
example
of
how
MEMEX
can be
used
in
a
typical
system.
The system
controls a robot
arm
working
on an assembly
line.
It
has sensors
to
input data
concerning
the
equipment
to
be
worked
on.
The
data
gathered from
the
analog
sensors
is
temporarily stored
in
the
system. Calcula-
tions
are then
performed on
it
and
instructions
are output
to
the robot arm.
The main
memory
of
the
system
consists
of
56K
of
ROM
and
8K
of
RAM.
This
is
divided
between
the
processor card
and
the
7704 memory
card.
The
8K
of
RAM
is
used
for
ma-
nipulating
data,
scratchpad
RAM,
and
for
the
subroutine
stack.
More
RAM
is
therefore
needed
to
store
data
as
it
is
received,
until
it
is
used.
A
second bank
of
memory
is
used
for this
purpose and
the
7706
resides
in
this
bank.
The
7706
resides
in
the
same
address
space
the
7704
occupies.
Only one
card
is
enabled
at
a
time,
however.
The
processor has
an onboard
I/O
port
used
to
drive the
MEMEX
line.
By
setting
the
MEMEX
line
either
high or
law, the
proc-
essor
can choose which
card
is
enabled.
The
memory
on-
board
the
processor card
itself
is
permanently
enabled,
that
is,
it
ignores
MEMEX.
The
processor
can enable
the
7706 when
it
is
receiving
data
and
store
the data
there.
It
can
then
move
the
data
in
blocks,
through
the
RAM
on
the
processor
card,
to
the 7704.
There
it
can
perform
calculations
on
the
data.
By
manipulat-
ing the
MEMEX
line
the
processor
can choose which bank
ol
memory
it
is
working
with
at
any
time.
3-4
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