Circuit Description, Fault Finding; Central Processing Unit, Lec Bus Interface; Unit; Modulation Interface; Unit - Philips PM 5390 Service Manual

3-1
3.
3.1.
CIRCUIT DESCRIPTION,
FAULT
FINDING,
PM
5390
CENTRAL PROCESSING
UNIT, lEC
BUS
INTERFACE; UNIT
1, fig.
37
The CPU
of the
PM
5390
contains the
8085
microprocessor, the
program and
data
memory
and
the
output ports for the
modulation
interface.
The
8085
microprocessor has
a
multiplexed address/data bus
ADO-7
and the address bus
A8-A15.
1C
317
latches
the address information
from
ADO—
7
by
means
of the
signal
ALE
(adress latch enable).
This
address information
at
the output
of 1C
317
feeds
the address inputs of the
program
memory,
ICs
306/311 and the data
memory,
1C
313.
The more
significant
address
lines
A8-A11,
necessary for
the
program memory,
are directly fed
from
the processor to the
memory
chips.
The
address lines
A12-'
A14 from
the processor are
decoded by
the address
decoder
IC
320
to 'chip enable'
/
'chip select
signals for the
memory
circuits,
ports
and keyboard
interface.
The
three Input
lines
contain
a
binary
information
which
is
formed
to
a
Tout-of-8 signal at
the
output
lines
of
this
decoder.
The
solder
switches
C
and
D connect pin 21 of IC
306
either
to
+5
V
or to the address
line
A1
1
to select
the
PROM
type
2716
or
2732
for this
socket.
The OR-gate
312
attaches the signals
RD
and
10/M
to
the control signal
OE
{output
enable) for
the
two
PROMs.
This
line
being 'low'
enables informations
from
the
PROMs
to
be read
by the processor.
Corresponding to
f
ied several
times
In
case of faulty
modifications
and technical
improvements
during production the software
was modi-
(indicated
by
labels
on
!C
306,
IC 31 1/unit
1
).
PROMs normally the
same
software has to
be
replaced. Please
order loaded PROIvls
directly via
Philips
Supply
Center Service,
Hamburg.
The
integrated circuit
318
is
a
multifunction chip with
a
RAM
of
256
bytes,
two 8
bit
and one 6
bit
input/output ports
and
a
programmable
timer.
The
RAM
memory
is
used
by the processor as
working
storage. Ports
A
and
B send control signals
from
the processor to the modulation interface,
unit
3.
The
third
port
(C)
senses the states
of the solder switches
E and
G
which
indicate
the version of the
instrument (G for
PM 5390
S)
and of the
lines
OLOC
and
ODVD
from
the
I
EC
bus controller
305.
The
timer within IC
318 generates
sweep
intervals,
which
result
from
a
counter value loaded
by the
pro-
cessor into
the timer
and counted
down
with the
30
kHz frequency
of IC
302.
The
timer
output 318.6
sends the information 'counted
down'
via
NOR-gate 307
to the
RST
5.5 input
of the
processor.
When
this
interruption
is
received the
processor
will
load
the timer again with a value
according
to
the required
sweep
interval.
The
resolution
of the
sweep time adjustment
is
—with the
clock frequency
of
30
kHz-
1/30
000
= 33.3
/is.
Timer control
and data handling with
the processor
are
performed by the control inputs
CE,
RD,
WR, 10/M and
ALE.
The
integrated circuit
313
is
a
further
RAM
memory
with
a
capacity of
128
bytes.
This
CMOS RAM
stores
the parameter
settings;
it is
supplied
by the
built-in
battery
(NiCd accumulator)
805
and stores
the parameters
when power
is
switched
off.
The
battery
can be switched off
by means
of switch
841
at
the
rear
of the instrument.
Attention:
The
storage
time
is
dependent on
the charging state
of the battery:
Storage time
charging
time
1
day
1
hour
5 days
3 hours
10 days
8 hours
mains supply
switched off