a3p250 Actel Corporation, a3p250 Datasheet - Page 25

• Manufacturer Part Number: a3p250
• Description: Proasic3 Flash Family Fpgas With Optional Soft Arm Support
• Manufacturer: Actel Corporation

Guidelines
Toggle Rate Definition
A toggle rate defines the frequency of a net or logic element relative to a clock. It is a percentage.
If the toggle rate of a net is 100%, this means that this net switches at half the clock frequency.
Below are some examples:
Enable Rate Definition
Output enable rate is the average percentage of time during which tristate outputs are enabled.
When nontristate output buffers are used, the enable rate should be 100%.
Table 2-15 • Toggle Rate Guidelines Recommended for Power Calculation
Table 2-16 • Enable Rate Guidelines Recommended for Power Calculation
Component
α
α
Component
β
β
β
1
2
3
1
2
•
•
The average toggle rate of a shift register is 100% because all flip-flop outputs toggle at
half of the clock frequency.
The average toggle rate of an 8-bit counter is 25%:
–
–
–
–
–
–
Bit 0 (LSB) = 100%
Bit 1
Bit 2
…
Bit 7 (MSB) = 0.78125%
Average toggle rate = (100% + 50% + 25% + 12.5% + . . . + 0.78125%) / 8
= 50%
= 25%
Toggle rate of VersaTile outputs
I/O buffer toggle rate
I/O output buffer enable rate
RAM enable rate for read operations
RAM enable rate for write operations
v1.2
Definition
Definition
ProASIC3 DC and Switching Characteristics
Guideline
Guideline
12.5%
12.5%
100%
10%
10%
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