Pioneer KEX-70 Service Manual page 9

* Display Control Section
A dynamic lighting system is adopted for the PD7004 display
with the LEDs being lighted in synchronization with the D1
through D6 (PD7004 pin 28 through pin 23) digit signals. A
sweep is performed in a period of about 3 msec. The digit
signals, used to indicate the digits (D1 = 1st digit; D2: 2nd
digit), are fed out from PD7004. The LEDs employed for dis-
playing the numbers are composed of 7 segments and, with
the addition of the dot [.], the 8-segment output is fed out
from the |C, the required segments of the LED for lighting are
synchronized with the digit output and segment output and
turned on, in each case at a period speed of 3 msec, with a
sweep being performed from the highest digit to the lowest
digit.
The above process is explained using Fig. 10 D1 through D6
are active at ''L" and S1 through S8 are active at 'H''. If the
description is simplified and confined to one LED, then, as in
Fig. 10, the LED lights only when the digit output is '"L" and
the segment output is '""H."
+5.8v
Q22~ Q27
On
Display
Sn
es jy be
Fig. 10
4 => Cy 48 Va 5c}
More specifically in the above figure when digit output Dn (iC
output) is ''L,'' the Q23~Q27 Darlington pnp transistors turn
ON and when the segment output Sn is ''H,"" IR2403 and Q37
turn ON, segment 1 of the LED lights. For instance, when the
first digit output goes to ''L'"', and segments (2) and (3) go to
"HU a "is indicated and lighting is repeated as in Fig. 12 at
a speed of 3 msec.
Distributing a signal to multiple digit lines by turns is called
dynamic lighting.
In the dynamic system, much fewer IC pins are used than with
the static lighting system where each of the segments is
lighted with a DC voltage. However, the dynamic signal
which causes the lighting is a 5Vp-p square wave and so care
must be taken lest it should not interfere RF and power supply
circuit.
The frequency, clock, band and channels are indicated by the
above method.
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