Repair manual

2-18
THEORY OF OPERATION
interface, it interprets (decodes) them and then directs the specified
operating function of the Digital Palette - downloads pixel image
information from Dynamic Memory to Video Memory, correctly
positions the filter wheel so that the specified color filter is placed
between the film frame and the CRT display screen, opens the attached
camera back shutter, exposes the pixel image information, closes the
attached camera back shutter, ejects or advances the film frame.
The instructions that the microprocessor receives are in the
microprocessor’s own vocabulary, known as the microprocessor’s
instruction set. Refer to the Parallel Port Interface Specification Manual
for detailed information pertaining to the instruction set format from the
host computer.
The Microprocessor operating features include:
1) Programmable Timers
2) Programmable Interrupt Controller Lines
3) Device I/O Select Lines
4) DMA Controller Channels
5) Programmable Memory
The following paragraphs describe each of the microprocessor features.
1) Programmable Timers
The microprocessor contains three 16-bit programmable internal
timers: Timer 0 (TIMRO IN/OUT), Timer 1 (TIMR1 IN/OUT),
and Timer 2 (TIMR2 - No Output Lines). Table 2-2 lists and
describes the function of each of the microprocessor ‘s internal
timers.
Table 2-2. Microprocessor’s Internal Timers
Timer Function
Timer 0 (TIMRO) This internal timer generates the Horizontal Synthesized
Sync (/HSYNC) signal. It is used for diagnostic purpose to
verify that the pixel frequency synthesizer is functioning
properly.
Timer 1 (TIMR1) This internal timer generates the Horizontal Sync
(XTALHS) signal. It is programmed to run from the
internal clock.