Introduction - Fluke 93 Service Manual

CIRCUFT DESCRIPTJONJS
3-7
3.3.3
MICROPROCESSOR
circuitry
(p^P)
•
Introduction
The
ScopeMeter
is
controlled
by
a single
chip
microcomputer
with
on-board
ROM
(called
Mask
ROM
In
the following
text).
TNs
microprocessor controls the
total
system
operation
and communication
between
the
ScopeMeter and
the outside world (key pad,
RS
*232-0
interface).
It
also controls the
communication between
Internal
system components.
*
Detailed
circuit description
See
figure
3.2
and
circus
diagram A1
(figure
1
0.2).
The ScopeMeter uses an
Intet
83C196
microprocessor D1201,
with
on-board
Mask-programmed
ROM
(Mask ROM).
This microprocessor
has an
S-bIt
data bus and a
16-bit
address
bus.
The
lower
B
address
bits AO..,
A7
are
combined
with the
data
brts
(multiplexed
data
bus).
ADDRESS
LATCH
D1210
is
used
to
separate data
bits
and address
bits.
The
microprocessor's
Mask
ROM
contains the
startup
software and a
diagnostic kernel
test (see
chapter
7).
It
also contains the
software necessary
to
drive the
serial
interface
and
to clear
and
program
Rash ROMs.
The
two
Flash
ROMs
(FRO
Ms)
D1207
and
01208
contain the system
software.
The
FROMs
are
directly
connected
to
the microprocessor
via
the
datand address
busses.
The microprocessor
addresses the
RAMs
via
the
D-ASIC
(D1203).
The
microprocessor
contains
five 8-bft
I/O
ports.
Port 3
and 4
share
their bits
with the
data
and
address
busses.
The
other
I/O
ports
0,1,2
are
used
for
vanous
purposes. For example: reading
the
keypad, operating
tfie
RS-232-C
interlace, battery voltage sense, switching
Ihe
power
on/off, etc.
Keypad
dreuitry
The
keypad
circuitry
consists
of five shift registers,
01601...D1606, each
of
which has
eight Inputs.
These
inputs are
normally kept "high"
by
S6 KIJ
resistor
arrays conr\ected
to
the
+SV
supply voltage.
Whenever
a key on the keypad
Is
pressed, the corresponding
line
is
connected
to ground,
resulting
in
a
"low" signal.
All
signals are clocked
into
the
shift
registers (with
the
FRONT.CLOCK
and
FRONT.
LATCH
signals).
Then
they are
converted
into
two
signals
FRONT
DATA1
(shift
registers
D1603, 01604,
D1606) and
FRONT.OATA2
(D1601
andDl602).
Opi/caity isolated
RS-232-C
interface
The
serial
communications
circuitry,
which
is
built Info
the microprocessor,
Is
used
to operate the
infrared (IR)
RECEIVER
and
TRANSMITTER
of
the
ScopeMeter. For
this
purposes
stripped version
of
the
RS-232-C
protocol
is
used.
Only
the
TXD
(transmit data)
and
RXD
(receive data)
lines
from
the
RS-232-C
standard are used.
The
IR transmitter
LED
HI
201
is
driven
directly
from
the
TXD-not
pin of
the microprocessor.
If
a
"0"
IS
transmitted, the
LED
lights.
The
IR receiver
uses
operational
^plifler N1301
to
power
the collector of phototransistor
HI
202.
If
any
IR
light
Is
received, the phototransistor
will
drive
VI
207
in saturation. This results
In
a
"low"
RXD
line,
interpreted by the microprocessor as
a 'T.
Battery
sense
circuitry
The
battery
voltage
-V6AT
generated on
the
analog
unit
is
amplified
by -2/3 at operational amplifier
N1301
.
The
resulting signal
BAT.LEVEL
Is
connected
to
an A/D
converter
Input
of
the
microprocessor.
In this
way
microprocessor can
monitor the
battery voltage
level.
If
the battery
voltage
level
drops below
4.4V, the
microprocessor generates the
BATTERY
LOW
Indication
on
the
LCD.