Repair manual

2-19
THEORY OF OPERATION
Table 2-2. Microprocessor’s Internal Timers (Con't)
Timer Function
Timer 1 (TIMR1) The XTALHS signal is used to drive the phase detector of
(Con't) the pixel clock frequency generator.
Timer 2 (TIMR2) This internal timer generates a 1 msec interrupt signal that
is used for program timing. IT IS ONLY USED FOR
INTERNAL COUNTING. IT HAS NO
INPUT/OUTPUT LINES.
2) Programmable Interrupt Controller Lines
The microprocessor has four external interrupt controller
lines. It also has number of internal interrupt sources such
as internal timers and DMA controllers. Refer to the
paragraph 1 for a description of the internal timers and to
paragraph 4 for a description of the DMA Controllers.
Table 2-3 lists and describes each of the microprocessor ‘s
external general purpose interrupt controller lines.
Table 2-3. External Interrupt Controller Lines
Interrupt Controller Line Function
Interrupt 0 (INTO) This interrupt line generates the Centronics Port
Interrupt (CPRTINT).
Interrupt 1 (INT1) This interrupt lines generates the SCSI Port
Interrupt (SCSIINT).
Interrupt 3 and 4 These interrupt lines are not used at this time. They
(INT3 and INT4) are connected to the external bus and are available
for devices on expansion boards.