Filter
Top Products
Theory of Operation
3–64
1780R-Series Service Manual
Rotary Encoder / Decoder. U441 is the decoder for the optical rotary encoder on
the touch panel. U441 compares the current inputs to CHA and CHB to the
previous reading and, if there is a difference, starts an up/down binary counter.
The counter output is transferred to an output register for the Master MPU to
read. The SEL input is held high to set the register to 8 bits.
Beeper. U530 is a timer connected in a multivibrator configuration. Its output,
pin 3, drives a piezoelectric transducer. When Q2 of latch U531 is low, U530 is
held off. The frequency of the multivibrator is controlled by Q3 and Q5 from the
latch. The latch is clocked when both WRL and CSREL inputs to U310C are
low.
Front Switch Panel. (Diagram 23) Switch closures couple SCANL0 through
SCANL7 to RL0 through RL2, which is read by the Keyboard Driver on the
Annex, Diagram 24. LEDs on the front touch panel are matrixed with the
+voltage on the FANODE (0-4) lines and the cathodes connected to the FCATH
(0-7) lines.
Touch Panel Output (Diagram 24). U288 is a 1 of 8 binary converter. Switching is
controlled by the SL0, SL1, and SL2 lines from the Annex circuits. The X output
of U288 is a serial output that drives the Touch Panel Output Amplifier. The
output of U297 is the TP Out signal to the Serial Parallel Shift Register on
Diagram 22.