4.3.2 Signal system for the 8253 block
Counters
#0,
#1
and
#2
of
the
8253 (programmable interval timer) work
as
a built-in clock.
These counters are used
as
mode 2 rate generators, and are all 16-bit binary counters.
51
Counter
#0
counts 31.25 kHz
input
pulses and delivers a pulse
to
OUT 0 every second; counter
#1
counts the
output
pulses
of
counter
#0
and delivers a pulse
to
OUT 1 every 12 hours; counter
#2
counts
the
output
pulses
of
counter #1 and switches between 0 and 1
to
work as an AM/PM flag. See
FIGURE 4.9.
8253
OUT2
Counter
GATE2
#2
CLK2
12
hours
OUT I
8
D Counter
GATE I
I 7
#1
Do
CLK I
1 second
OUTO
Counter
GATEO
#0
CLKO
~----
31.25 kHz
FIGURE
4.9 Signal system for the 8253 block
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