Trio™ Service Manual
0070-10-0591-01
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Theory of Operation
Hardware Overview
1.2.6
Keypad Board
P/N 0671-00-0064
FIGURE 1-8
Keypad block diagram
1.2.6.1
Detailed Description
This module detects keypad and encoder input signals, converts them into code and transmits
the code to the Host CPU board. The Host CPU board sends commands to the keyboard
which in turn controls the indicator and audio process circuits, activating audio and visual
alarms accordingly.
CPU
The Keypad Board's CPU is responsible for the following functions:
• Detects keypad and encoder input signals
• Controls LED status
• Controls Audio Process Circuit
• Regularly zeroes Watchdog Timer
• Communicates with main board.
Key Test Points
NO.
NAME LOCATION
FUNCTION
1
VCC
P4.4
Power input, range: 4.8~5.2V
2
GND
P4.5
Power supply and signal ground
3
RST
U1.10
CPU reset signal. At low level(<0.3V) when
operating normally
4
Crystal oscillator
X1.1,X.2
CPU crystal oscillator. Sine wave signal
(1.5~3.5V) when operating normally
Watchdog
ENCODER
KEY
CPU
(PIC16F73)
RAM
192 X 8
FLASH
4K X 4
Main Control
board (Host CPU Board)
Audio Process
Circuit
SPEAKER
LED
