Jameco Electronics Rabbit 2000, User Manual

Page: 236 / 349

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.
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
17 58.8 18 55.5
Spreader only
normal
20 50.0 21 47.6
Spreader only
strong
21 47.6 22 45.4
Doubler only
(8 ns delay)
19 52.6 20 50.0
1 > (clock low -
clock high) > 0
Doubler only
(internal 50%
clock)
20 50 21 47.6
1 > (clock low -
clock high) > -1
Spreader
normal with
doubler
(8 ns delay)
21 47.6 22 45.4
4 > (clock low -
clock high) > 2
Spreader
normal with
doubler (8 ns
delay), internal
50% clock
24 41.6 25 40.0
1 > (clock low -
clock high) > -1
Spreader only
strong
21.5 46.5 22.5 45.0
Spreader strong
with doubler
(8 ns delay)
23 43.5 24 41.6
8 > (clock low -
clock high) > 6