Theory of Operation
Publication 21555, Rev. E, September 2002
3-11
3.6.2
CPU & Memory
3.6.2.1
Processor
The Interface circuitry of the Processor board uses an 8 MHz 68HC000 CMOS processor (U7). See the
latest Motorola data sheet for further information on this chip.
3.6.2.2
Real Time Clock/Timer
U1 generates the system tick for a pSOS kernel operating system. It also adds time and event capabilities
to the application code. For further information, see the latest Hitachi 146818 data sheet.
3.6.2.3
Interrupt Controller
The processor uses seven levels of auto vectored interrupts. U6 encodes the priority levels for the
processor. Three levels of auto vectored interrupts are available to the user. These are signals AVINT4,
AVINT3 and AVINT2. The higher numbered interrupt signal has the higher priority. The user accesses
these signals from the P5 pin connector on the Processor board.
3.6.2.4
Bus Error Timer
U2A divides down the VXI 16 MHz clock for the 8 MHz processor. U2B is used to generate a bus error
signal if timeout occurs before data transfer acknowledgement. The timer generates this signal if a
processor access cycle exceeds 16 microseconds.
3.6.2.5
Local Address Decoders
U17 and U18 are address decoding GALs. These circuits generate the chip selects and the control lines
for access to the RAM, ROM and other functions.
3.6.2.6
Drivers & Transceivers
U26 and U27 transceivers drive the local data from the processor bus to the shared bus and vice versa.
The processor address lines are driven by U21 and U22 to the shared bus.
The VXI gate array, U28, enables these buffers.
3.6.2.7
Local Memory
U9 and U11 are two 32K X 8 static RAM chips on the processor bus.
3.6.2.8
LED Drivers
The actual LEDs are located on the Analog PC Board. U32 is a one-shot used to widen the pulse of the
VME A16 and A24/A32 signals. U34 is used to drive the RUN, HALT, MODID, A16 and A24/A32
LEDs. The FAIL LED is driven directly from the VXI chip. The TRIGGER LED is driven under
software control.
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