GE_OEC_9600_C-Arms

Image System 5
MICROCONTROLLER
U16 is a CHMOS 16 bit 80C196KC microcontroller. The 8 MHz. reference is provided by
crystal oscillator Y1. LED DS1 blinks on and off during normal operation providing a
visual indication that the microcontroller is operating and executing code.
Port 3 (pins 53-60) of the microcontroller is a multiplexed address/data bus. U12 latches
the low address byte (A0-A7) on the falling edge of ALE, address latch enable (pin 62 of
U16). Port 4 (pins 45-52) is permanently selected for the high address byte (A8-A15) by
grounding the signal “BUSWIDTH” (pin 64 of U16).
EPROM
U15 is a 32K x 8 EPROM programmed with operating code for the microcontroller.
GAL
U13 is a GAL (gate array logic) used in address decoding to provide the chip select (CS)
signals for the following:
EPROM - U15
EEPROM - U7
SRAM - U10
INPUT LATCH - U14
OUTPUT LATCH - U6
MOTOR LATCH - U11
STATIC RAM
U10 is a 32K x 8 static ram, used by software for storage of variables. It was added to
enhance the amount of memory available for the microcontroller.
EEPROM
U7 is a 2K x 8 EEPROM used to store the calibration data for the Normal, MAG1, and
MAG2 field sizes of the collimator iris. E5 is used in the iris calibration procedure.
Details of this circuitry are discussed in the Collimator Motors and Collimator Iris
Calibration sections that follow.
WATCHDOG
U8 provides the reset and “Watchdog” functions. Microcontroller U16 is reset when pin
16 is pulled low during power-up, power-down and during low-voltage brown-out
conditions. Pin 7 of U8 is toggled by the output of microcontroller U16 pin 23 every 150
ms to prevent the watchdog from timing out. If a software failure should cause the
watchdog to time-out, the reset output from U8 pin 6 will go low for 250 ms and reset the
microcontroller. The Master Reset signal (MRESET*) from the Technique Processor
PCB can also initiate a reset. This would occur if the reset switch on the Technique
Processor PCB was pressed. Jumper E8 is removed only in the factory for testing and
must be in place for proper operation.