Led Display Circuit; Led Display Method - Toshiba 1550 Service Manual

5.4 LED Display Circuit

(1) LED display method

Described here is the LED for "dual-page copy-
ing" display when "DP" comes ON. When the
DSPON0 signal goes to "L" level, transistor Q2
is turned ON. When pin 7 of the IC (D15) goes
to "L" level, electrical current flows through the
transistor to the LED (DP) from +5V. In other
words the LED (DP) comes ON.
(2) The actual circuit is controlled as follows:
• DSPON0 and DSPON1 signal goes to "L"
level alternatively for 8 msec.
• Q1 or Q2 goes to the ON condition when
the DSPON0 or DSPON1 signal is at "L"
level.
• The LED ON/OFF signal from LGC is in-
putted to the IC SIN (pin 5) terminal via the
DSPDAT signal (serial data).
• LED ON/OFF signal is outputted in parallel
to D1-D16 output terminal, after being in-
putted to IC in series.
1550/1560 DISPLAY
R4
DSPON0
"L"
8 msec 8 msec
TR2
DSPON1
OFF
TR1
DSPON0
ON
DSPDAT
D1
LED "00"
LED "01"
5 - 4
+5V
Electrical
R3
current
"L"
G
Q2
R28
(LP32)
PWA-PNL
TR2
ON
TR1
OFF
ON
ON ON
Mar. 1998 © TOSHIBA
D15
7