Philips PM2519 - Page 38

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2.4.6.
2.5.
RAM
The external RAM in the PM 2519 is an 12C device; data and address are transferred serially via two lines.
The organisation internal is 128x8 bits. In the RAM all the calibration values are stored and also the preset
values for each function. A battery G1719 supplies the RAM if the power is switched off.
NOTE:
To
prevent
loss
of
information
during
battery
replacement,
the
latter
can
be
done
when
the
voltage
at
7p1005
and
Tp1007
is
present.
DISPLAY
The OQ 0070 is a single chip silicon-gate C-MOS circuit, designed to drive a Liquid Crystal Display with up
to 54 segments in a triplex manner. Reference voltages are internally generated with temperature compen-
sation. A 2-line 12C bus structure enables serial data transfer with the microcomputer.
A LCD is an a.c. device. Therefore, for multiplexing the information of the segment line is important for
each segment that will be driven by that line.
When triplexing (in the PM 2519) is used, each backplane is driven one third of a timeperiod. To ensure a
longer lifetime, the driving pulse is inverted every time period.
The data derived from one data output is fed to three segments.
To these segments also one of the backplanes is supplied.
The voltage across a segment will determine if it is lit or not.
The following is an example.
DATA
f SEGMENT'B“AND “C'WILL LIGHT
BPI BP2 BP3
er
sP2 pil s= — i
ers adh ou
al L_
DATA
a eee
VOLTAGE
OVER A
VOLTAGE
OVER B LI i
Pile PL a
VOLTAGE
OVER C
pa L Ly
STeete
840727
Fig. 2.17. Signals LCD drivers