The Main
Interconnect
Board
The main
interconnect
board
contains
most
of
the
operating
logic for
the MicroLab|.
In
this
part
of
the
manual, we'll talk
about the
following
parts
of
the
main
interconnect
board:
®@
communications
between
the
main
interconnect
board
and the
other
circuitry
@
memory
©
breakpoint
circuitry
@
serial
|/O
ports
@
keypad
and
display
logic
As
with
the rest
of
this
section,
the
text
refers
to
the
schematics
located at
the
rear
of
this
manual.
You'll find
it
helpful to refer to
the
schematics
while
you
read
the
text.
®
Ea
The main
interconnect
board
communicates
with
the
personality
card, the
keypad/display
board,
|/O
ports,
and
whatever
may
be
attached
to
the expansion connector
at
the rear
of
the
MicroLab
|.
All
lines
to
and
from
the
personality card
(J8060)
are
buffered. The lines to
the
expansion connector (J9060) are
buffered
wherever
possible.
However,
the
device
attached
to
the expansion
connector
should provide buffering
in
both directions.
Communications
Data
Flow
Notice
in
the bottom
left
corner
of
schematic
1
that
the
data
lines coming from
the
personality card are
attached
to
the
input lines
of
latch U7050.
Data
coming from
the
microprocessor
is
latched
through
U7050
for
timing
purposes. Data going to
the microprocessor
from
the
main
interconnect
board does not
pass through
U7050, but
instead
passes
through tristate
buffer U6050.
To
summarize, data comes
from
J8060,
through
U7050,
and
onto
BDO-BD7.
The main
interconnect
board
sends
data
from
BDO-BD7
through
U6050,
and
out to J8060.
As
youcan
see,
pin
11
of
U7050
is
tied,
through
an
inverter,
to
the
E
line from
the personality
card. The
E
line
is
the
master enable
line.
The microprocessor
on
the personality
card brings
E
low
after
all
other
control
and
data lines
are
stable.
Data
is
read
from
the
main
interconnect
board
with
a
combination
of
signals.
The microprocessor
forces
its
R/W
line high, which
is
connected
to
pin
5 of
U5030.
Pin
12
of
U5030 goes high any time
RAMC1,
RAMCO,
or
ONBDIO
from
the
personality
card goes
low.
Once
this combination
of
signals comes together,
buffer U6050
places the
data
from
BDO-BD7
onto
the
DO-D7
lines.
@
Theory of Operation—MicroLab
|
Instruction
Address
Flow
In
the
top
left
corner
of
schematic
1,
you
can
see
the
address bus
coming from
the
personality card. Address
lines
AO-A9
are
buffered
by
U8040
and
U1080.
Because
of
the
MicroLab
I's
limited
RAM
space,
only
address
lines
AO-AQ
are
needed
to
address
the
full
range
of RAM.
AO-A9
are fed
through
U8040
and
U1080
onto internal
address
lines
BAO-BAQ.
Notice
that
address
lines
A10-A15
are
not
buffered. They are
instead sent
to
the
breakpoint
logic,
where they require
no buffering. We'll
discuss
the
breakpoint
logic
later on
in
this
section.
Reset
Circuitry
A
While
we're
looking
at
schematic
1,
let’s
examine
the
reset
circuitry. The
MicroLab
|
can be
reset
by
one
of
two means:
you
can press the reset
button, or you can turn the
MicroLab
|
power
off
and then
on again.
The
RESET
key
from the
MicroLab
|
keypad
is
attached
to
pin 16 of
P3010
(at
the bottom
left
of
schematic
1).
When
the
RESET
key
is
pressed,
pin
16
of
P3010
goes
to
ground.
Grounding
pin
16
causes transistor
Q1014
to
shut
off.
When Q1014
shuts
off,
the
base
of
02012
goes toward
+5
volts,
turning
on
Q2012.
This
causes
the
RESET
line
to
the
personality
card
and
main
interconnect
board to
go low.
Notice
a
100-ohm
resistor
(R3011)
in
line with
pin
16.
This
resistor
limits
the
amount
of
current that
can
flow
through
the
RESET
switch
and prevents the
switch contact from
being
welded
closed.
When
MicroLab!
power
is
turned
on,
capacitor C3012
begins
to
charge through
R2012.
This
action forces the
base
of
Q1014
low,
and
also
causes
a
reset.
Diode
CR2013
forces
the
capacitor
to
discharge faster when
the
power
is
shut
off.
memory
<2>
FEB]
There
are
several things
to
remember
when
dealing
with
the
MicroLab
|
RAM:
the
RAM
is
configured
as
4K-byte
memory
when
using 8-bit personality cards;
RAM
is
automatically reconfigured
into
2K-word memory when
using 16-bit
personality
cards; and,
a
1K-byte segment
of
RAM
is
software
relocatable.
8-bit
Operation
Notice
on
schematic
2
that there
are eight
memory
devices
Also notice
that
the
devices
are
connected
in
pairs. U6040
and
U4040
make
up
a
1K
x
8-bit
pair,
U5040 and U3040
make up
another
pair,
U44060
and
U4050
make
up
a
third,
and U3060 and
U3050
make
up the
fourth
pair.
Each pair
is
controlled
by
a
RAMC
line
from
the personality card
as
shown
in
Fig.
5-4.
Summary of Contents for 067-0892-00
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