Vector Graphic Bitstreamer II User Manual - page 43
To deternine
the source of t..'1e
interrupt within a 3itstreamer II board,
software must poll potential interrupt sources on the board.
If none of the
825l's are active, then the clock must be the source.
After
dIe
CPU responds to an interrupt
by transf9rring
control
to the
interrupt
service
routine,
the source
of the
interrupt
must
be cleared
before re-enabling interrupts with ~he EI instruction.
To clear one
of the
8251
interrupt
sources,
software
must
input from the I/O address of that
8251.
The inputted byte does not have to be used
by the software
for any
purpose.
To clear the real time clock interrupt latch, software must input
from Parallel Channel 3.
If a spurious
interrupt
is received,
for which
software cannot determine a source, it is a good idea to clear all potential
interrupt &~urces.
The
eight
5-100
VI
lines
are
available
on the board for communicating
interrupts to a'1other ooard for prioritization or other kinds of ?rocess ing
before
reaching the CPU.
At this time, no Vector Graphic board is designed
to make use of such signals.
If you do make use of them on another
board,
you would
not
tie any of the pads
in area A to pad A-8
(PINT).
Instead,
jumper tl1edesired pads in area A to the pads in area K.
Each pad in area K
corresponds to one of t..'1e
VI lines VI0 to VI7, as follows:
VI Line
Area K pad
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
VI Lines Available in Area K
Table 11