ACT apricot - Page 65

TIMER
When the counter is programmed to operate in Mode 3
using
an odd count value, the frequency of the output is
equivalent
to 2 MHz divided by the count value as for an
even count value, but the output waveform is
asymmetrical.
The asymmetry being more pronounced for
low
count values (high output frequencies). If the value is
odd,
the counter output remains at logic high for (N + 1 )/2
clock pulses
and remains at logic low for (N-l )/2 clock
pulses as
illustrated in the timing diagram Figure 3, where
N represents the count value.
CLOCK
I
OUTPUT I 4
2
4
2
EVEN COUNT~rl ----...:~--i
STATE
(N=4) L-- ___ ---'
4
OUTPUT It--- (N+D/2 -- .... - (N-D/2---t1
2 I
I
L
ODD COUNT~ ,-----
STATE
(N=5)
Figure 3.Mode 3 timing diagram