9600 Service Manual - gmecorp-usa.com

Workstation Control 5
CONTROL PANEL PROCESSOR PCB
Microprocessor
U5 is an 80C196KC microcontroller running at 12Mhz. Y1 is the crystal oscillator
providing the 12MHz clock signal. This can be measured at TP11.
U24 and associated circuitry comprise a watchdog circuit driven from microcontroller U5,
pin 20. This line must be toggled every 1.6 seconds to keep the watchdog from timing
out and issuing a reset to the microcontroller. Power monitor U24 is also used as a reset
generator to monitor the +5 volt supply to microcontroller U5. The reset output is held
low when the +5 supply is less than approximately 4.65 volts. This low will generate a
reset to microcontroller U5 and also PAL U4.
U13 is a four channel push-pull driver used to drive an externally mounted piezoelectric
tone generator. It is driven from microcontroller U5 pin 28 through inverter U11
pin 12.
A beep is sounded when the Boot process is complete and the Control Panel Interface
PCB, QWERTY keyboard, front panel, and TrackPad panel are successfully enabled.
Memory and Addressing
PAL U4, and latches U2 and U14 are used for address decoding.
U10 is the boot EPROM (32K bytes) containing the code for microcontroller U5.
U1 is read and write Static RAM .
Control Inputs and LEDs
The Control Panel Processor PCB receives command and text signals from the:
• QWERTY Keyboard
• Track Pad Panel
• Front Panel
The force sensitive resistor (FSR) on the Track Pad pointing device provides four analog
signals (S, E, N, W). These signals are input directly to microcontroller U5.
The microprocessor scans the Qwerty Keyboard, Front Panel keys, and Track Pad
Panel keys through the row output latches U18 and U22. The microprocessor detects
which switch is pressed through keyboard column input latches U15 and U23. Software
continuously scans the keypad to determine if any keys have been pressed.