Philips PM2517E - Az; Ds1, Ds2, Laen; Ovr; Pol

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Az,fr lAuto
zercl
The
auto
zero signals
are
switching
the
input
voltages to the
inputs
of the
ADC
(Refer
to 3
3 3
ADC and
3.3.4.2.
Control
Logic).
The AZ
and
AZ
are
determined
by the clock
and
the
12.888 timer'
One
AZ
period
is:200
msec.
OVR
In case of overrange. which means that
the result
is ) 10.000
counted
clockpulses,
siqnal
OVR
becomes
active
(logic
1
).
When
a
manual range
is selected,
signal OV
R
will
cause
the displav
to
be switched
to overrange
(displav
O).
DSl, DS2,
LAEN
DS1,
DS2
(digit
select)
anC
LAEN
(latch
enable)
are
used
for timing
of
the
display
unit.
(Refer
Fig. 25
)'
Signals
DSl
and DS2 are
s€lecting
the digits
for serial
display'
Signal
LAEN
is used for
latching
the BCD
information
for
a LX
display
LAEN
is not used in the
PM
2511
E
AO, A1, 42,
A3
Signals
AO,
A1, A2, ,A3 are
the data information
from the
OO
0059'
The signals
appear
in
bit
parallel
and
word serial
informataon'
Together
with the control
signals
DSl,
DS2 and
LAEN,
the data
is used
for
serial
display'
POL
The state
of the
polanty
signal
(logic
0
= -,
rog
1
=
+)
is determined
by the state
of
the
incoming
data
signal.
when
more
up than down
puises
are
counted
in the
1st measuring
penod
this
means
+ polarity.
When
more dordn than
up
pulses
are counted
this
nreans
-
polarity
'
The
detection
is made by
the
polarity
detection
circuit
inside
the OO 0059'
3.3.5.
Display
unit
N2
(Fig.25
and
54)
3.3.5.1. Genercl
The displav-section
consists
of
four 7-segment
LEDs a BCD
to
7-segment
decoder,
a dual
1 of
4 decoder/
demultiplexer
for serial display
and the
polarity/unit
indication.
The
display section
is built
on one
small
p.c.
board
N2. The
interconnection
between
the
units in the
PM 2517
is made
by a 2g'pole
interconnectron
strip.
Of the strip
not all contacts
are used
in the
Pl\4 2517
E.
ln the
PlVl 2517 X all
contacts of the
strip
are used.
3.3.5.2.
Data 43,
42. Al
,
A0
Thedatabitpara||e|-wordseria|isderivedfromthedigitaIcontro||coo0059andis5upp|iedtotheBcD
to
7-segment
decoder.
As a serial
displav
ts used
the
data
is switched
with
the
speed
of clock signal
DS
1
The data
is switched
in the
following order:
t02,
t03,
to0 and
101
(Refer
to the
timing
diagram
Fig
25)'
The decoded
data
trom
the BCD
to 7-segment
decoder
is supplied
to
the
LED'5
Dependent
to
the
decoded
signals
DS'1 and
DS 2
the correct
LED's
are switched
on'
3.3.5.3. Elank display
(40
sec. circuit)
Via the btank
input
of the
HEF4511
lD
7O1l4),
it
is
possible
to
blank
the
data
in the
displav
The
decimal
point, polarity
and unit indication are
not blanked. Blanking the
display is used
in the STAND
BY
position
of
the
PM
2517
E.
When
push
button DISPLAY
is
activated,
signal BL becomes
logic 1 and the
display
is allowed
to
light
After
about 40
sec. delay is energized in the circu it built-up
of V 7051706,
R 719/720/721 /
on
unir
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