October 2002
Intermediate to advanced
430 pages
14h 57m
English
Content preview from Embedded Systems Design, 2nd Edition
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Basic peripherals 137
watchdog timer where the output is connected to a non-maskable
interrupt line or a system reset.
0000004
0000003
0000001
0000000
Load initial value
(0000004)
Count
down
by 1on
every
clock
cycle
O
utput goes lo
w
Clock
O
utput
0000002
Output goes high
Square wave generation
Hardware triggered strobe
Mode 5 is similar to mode 4 except that the retriggering is
done by the external gate pin acting as a trigger signal.
Generating interrupts
The 8253 has no specific interrupt pins and therefore the
timer OUT pin is often used to generate an external interrupt
signal. With the IBM PC, this is done by connecting the OUT signal
from timer/counter 0 to the IRQ ...