Theory
of
Operation—MicroLab
|
Instruction
This
low causes
the
output
of
U30308B
to
go
high.
The high
at
the output
of
U3030B
istied
back to
pin
10
of
U4090C.
Remember
that
RCO is
high. The
output
of
U4090C
(BREAKPOINT)
goes
low.
Notice
that
BREAKPOINT
is
tied
to
the
inputs
of
U2030A
and
U3080C.
Now,
depending
on
the states
of
the
IRE
and
SPE
lines,
either
a
breakpoint
interrupt
(BINT)
will
be
sent
to
the personality
card, or
a
special
key
interrupt
(BSP) will
be
sent
to
the personality
card.
Much
the
same
thing
would
happen
if
the
match
occurred
at U6080B. The
output
of
U6080B would go high, be
inverted
to
a
low at
pin
5
of
U4090B
and
pin 12 of
U3080D.
But
this
time, a high would be
present at the output
of
U2022C. Again, a low would be forced into
pin
5
of
U3030B,
and
a high
output
would
result.
This high
is
NANDed
with
RCO
at U4090C,
and
a
breakpoint
occurs.
Now
let's
look
at what happens
when
the
ORE
line
is
low.
AND. We'll make
some
of
the same assumptions as
before. We'll
assume that
a match
was made
by
U6080B,
and
that as
soon
as
RCO
goes
high,
the
output
of
U6080B
will
go high.
In
order to
demonstrate the
AND
operation,
and
prove
that
a
breakpoint
won't
occur
unless there are
two
matches, we'll
assume
that
a match
was
not
found
by
U6080A,
and
its
output
is
low.
Until
RCO
is
set
high,
the
outputs
of
U6080B,
U2030C,
and
U6080A
are
all low. As
before,
this
places
all
highs at the
inputs to
U3030B,
forcing
the
BREAKPOINT
line
high.
Now,
when
RCO
goeshigh,
the
output
of
U6080B
goes high.
This
high
is
inverted
and
fed
to
pin
5
of
U4090B
and
pin
12
of
U3080D. The
output
of
U2022C
is
high
(remember,
U6080A didn’t make
a
match), forcing
a
high at
pin
4
of
U4090B
and
pin
13
of U3080D.
So,
we
have
a
high
and
a
low at
the inputs
of
U4090B.
This
combination
keeps
the
output
high.
AtU4090A,
the
high from
U4090B
and
the
low
ORE
line
are
NANDed,
keeping
pin
5 of
U3030B high.
Remember,
we
need a low
at one
of
U3030B’s
inputs
to
create
a
breakpoint.
Let's
see
if
we can
find
another
way.
At
U3080D,
pin
13
is
high,
and
pin 12 is low.
This combination
forces
a high to input
pin
4
of U3030B.
And
since we
can’t
force
pin
3
low
until
one
of
the other
input pins goes
low,
no
breakpoint occurs.
No
breakpoint
is
possible
because two
matches
weren't
found.
In
other
words, an
AND
situation
didn’t occur.
What would
happen
if
the
outputs
of
U6080A, U2030C,
and
U6080B
were
all
high
when
RCO went
high?
First
of
all,
a
low
would exist
at output
pin
8 of
U2022C.
That
lowis
passed
on
to
pin
13
of U3O80D.
Pin
6
of
U6080B
is
high,
so
another
low
exists
at input
pin
12
of
U3O080D.
These two
lows are
combined
to
create
a
low at
pin
4
of
U3030B.
As
soon
as
pin
4
goes
low,
pin
6
goes
high. The
high
is
fed back
to
pin
10
of
U4090C
and
NANDed
with
the
high
RCO
line
to
force
the
BREAKPOINT
line
low
and
enable
either
BINT
or
BSP.
To
Summarize,
when
the
ORE
line
is
high,
either
U6080B
or
the U6080A/U2030C
combination
can cause
a
breakpoint.
When
the
ORE
line
is low,
an
AND
combination
must
exist
to
cause
a
breakpoint.
Next,
we'll
look
at where
the
RCO
line
comes
from.
Breakpoint
Delay
Counter
>
HA
The
Breakpoint Delay Counter
is a
presettable
ripple
counter.
A
binary value
is
loaded
into
the
A,
B, C,
and
D
inputs
by
the
Control Register
(U2070).
The
counter
is
then
clocked
by
the
BE
line
from
the
personality
card.
As
soon
as
the
internal binary value
has reached
“1,1,1,1",
the
RCO
(ripple carry out) line goes
high.
The delay,
then,
is
the time
it
takes
to
count
from
the
value
entered
to
the
maximum
value possible.
Because
the
comparator circuitry
is
asynchronous,
a
comparator
match
will
remain
stable
until
a
new
set
of
match
values
are
stored
in
the
latches.
This
gives
the
counter
time
to
count
out,
and then enable
the
interrupts.
Breakpoint
Status
And
>
fH
Control Registers
The Breakpoint
Status register
(U3070) indicates
to
the
personality card whether
a
breakpoint
has
occurred, and
indicates
the
states
of
BSPO-BSP6.
The
contents
of
the
Status register
are placed on
BDO-BD7
each time
a
breakpoint
occurs.
When
an
interrupt
occurs, the
personality card can
poll
the
Breakpoint
Status
byte
to
see
if
the
interrupt was
a
breakpoint
interrupt.
The Breakpoint
Control
register
allows
the
personality card
to
determine whether
two portions
of
the Breakpoint
Enable
logic will be ANDed or ORed
together.
The Control
register also determines where the
breakpoint interrupt
will
go
— that
is,
whether
a
breakpoint
interrupt
will
be
sent
to
the
personality card, or whether the
interrupt
will
be
sent
to
the
SPECIAL
key circuitry.
The Control
register's
third
function
is
to permit
the personality
card
to
delay
a
breakpoint interrupt,
by
loading
a
count value
into
the
Breakpoint Delay Counter.
The Serial
|/O
Ports
&
The
MicroLab
|
has
three
serial
|/C
ports:
a
terminal
RS-
232-C
port,
a
MODEM
RS-232-C
port,
and
a
cassette
port.
You'll find
the
logic
for
all
three
ports
shown
on schematic
3.
First, however,
we'll
cover the
Baud
and
Clock
Generator
circuit
shown
at
the
top
of
the schematic
3.
This
circuitry
serves
all
three
|/O
ports.
Summary of Contents for 067-0892-00
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