Jameco Electronics 3000 用户手册
User’s Manual
227
16.4 Maximum Clock Speeds
The Rabbit 3000 is rated for a minimum clock period of 17 ns (commercial specifications)
and 18 ns (industrial specifications). The commercial rating calls for a ±5% voltage varia-
tion from 3.3 V and a temperature range from -40 to + 70°C. The industrial ratings stretch
the voltage variation to ±10% and a temperature range from -40 to + 85°C. This corre-
sponds to maximum clock frequencies of 58.8 MHz (commercial) and 55.5 MHz (indus-
trial). If the clock doubler or spectrum spreader is used, these maximum ratings must be
reduced as shown in the following table. When the doubler is used, the duty cycle of the
clock becomes a critical parameter. The duty cycle should be measured at the separate
clock output pin (pin 2). The minimum period must be increased by any amount that the
clock high time is greater or less than specified in the duty-cycle requirement.
and 18 ns (industrial specifications). The commercial rating calls for a ±5% voltage varia-
tion from 3.3 V and a temperature range from -40 to + 70°C. The industrial ratings stretch
the voltage variation to ±10% and a temperature range from -40 to + 85°C. This corre-
sponds to maximum clock frequencies of 58.8 MHz (commercial) and 55.5 MHz (indus-
trial). If the clock doubler or spectrum spreader is used, these maximum ratings must be
reduced as shown in the following table. When the doubler is used, the duty cycle of the
clock becomes a critical parameter. The duty cycle should be measured at the separate
clock output pin (pin 2). The minimum period must be increased by any amount that the
clock high time is greater or less than specified in the duty-cycle requirement.
Table 16-7. Maximum Clock Speeds at 3.3 V [Preliminary]
Conditions
Commercial Ratings
Industrial Ratings
Duty Cycle
Requirements
(ns)
Minimum
Period
(ns)
Maximum
Frequency
(MHz)
Minimum
Period
(ns)
Maximum
Frequency
(MHz)
No doubler or
spreader
spreader
17
58.8
18
55.5
Spreader only
normal
normal
20
50.0
21
47.6
Spreader only
strong
strong
21
47.6
22
45.4
Doubler only
(8 ns delay)
(8 ns delay)
19
52.6
20
50.0
1 > (clock low -
clock high) > 0
clock high) > 0
Doubler only
(internal 50%
clock)
(internal 50%
clock)
20
50
21
47.6
1 > (clock low -
clock high) > -1
clock high) > -1
Spreader
normal with
doubler
(8 ns delay)
normal with
doubler
(8 ns delay)
21
47.6
22
45.4
4 > (clock low -
clock high) > 2
clock high) > 2
Spreader
normal with
doubler (8 ns
delay), internal
50% clock
normal with
doubler (8 ns
delay), internal
50% clock
24
41.6
25
40.0
1 > (clock low -
clock high) > -1
clock high) > -1
Spreader only
strong
strong
21.5
46.5
22.5
45.0
Spreader strong
with doubler
(8 ns delay)
with doubler
(8 ns delay)
23
43.5
24
41.6
8 > (clock low -
clock high) > 6
clock high) > 6