Yamaha DRX-1 Service Manual page 74

DRX-1
2. Display Board
2.1 Operation Unit DC (DC Part)
The core element of the operation unit DC is the
m i c r o c o n t r o l l e r T M P 8 8 C U 7 7 Z F [ 7 1 5 6 ] . T h e
TMP88CU77ZF is an 8 bit microcontroller fitted with 96kB
ROM and 3kB RAM and is responsible for following
functions:
• Integrated VFD driver
• Timer
• Evaluation of the keyboard matrix
• Decoding the remote control commands from the infra-
red receiver pos. 6170
• Activation of the display
• Motor driver
The system clock is generated with the 12MHz quartz
(Pos. 1153).
2.2 Evaluation of the Keyboard Matrix
There are 15 different keys on the display board. A resistor
network is used to generate a specific direct voltage value,
depending on the key pressed, via the resistors 3145,
3171, 3183 and 3194 on the analog/digital (A/D) ports
(7156 Pin 17, 18, 19, 20). Pressing keys simultaneously
may lead to undesired functions!
2.3 IR Receiver and Signal Evaluation
The IR receiver [7140] contains a selectively controlled
amplifier as well as a photo-diode. The photo-diode
changes the received transmission (approx. 940nm) in
electrical pulses, which are then amplified and
demodulated. On the output of the IR receiver [7140], a
pulse sequence with TTL-level, which corresponds to the
envelope curve of the received IR remote control
command, can be measured. This pulse sequence is input
into the controller for further signal evaluation via input
IRR [7156, pin 2].
2.4 Motor Driver Flap
The flap-motor is controlled via the 2 Port-Pins (MD1,
MD2) of the P (7156, Pin 12, Pin 100). The motor driver
part is constructed as a bridged dual power operational
amplifier.
Between the IC outputs (7120, Pin1, Pin3) and a
Boucherot circuit (2121, 3126) suppresses a spurious
3MHz oscillation from the output stage. The two ports-pins
(MD1, MD2) of the P are PWM-outputs and are controlled
in the following way:
74
Flap Motor:
MD1
off H
open H
close L
Duty Cycle 50% for OPEN and CLOSE
Duty Cycle app. 10% for CLOSE
Duty Cycle app. 10% for OPEN
Fig. 3
For the detection of the end-positions of the flap there are
two switches (1178, 1179) installed and the information is
evaluated from the P via the signals SW_1178 and
SW_1179.
Flap Switches:
SW1
open L
closed H
moving H
error L
2.5 Bi-Color LED (Standby and ON)
The STBY-LED is a red/green bi-color-LED and is
controlled via the STBYLED-signal of the P (7156 Pin 10)
in the following way:
Colour of STBY
LED
red
green
MD2
L
PWM(H)
PWM(L)
SW2
H
L
H
L
Status of the Set
STBY
ON