A3P030 datasheet(18/210 Pages) MICROSEMI

18 / 210 page

ProASIC3 Flash Family FPGAs

Re vi s i on 15

2 - 13

RAM Contribution—PMEMORY

PMEMORY = PAC11 * NBLOCKS * FREAD-CLOCK *

2 + PAC12 * NBLOCK * FWRITE-CLOCK *

NBLOCKS is the number of RAM blocks used in the design.

FREAD-CLOCK is the memory read clock frequency.

2 is the RAM enable rate for read operations.

FWRITE-CLOCK is the memory write clock frequency.

3 is the RAM enable rate for write operations—guidelines are provided in Table 2-17 on page 2-13.

PLL Contribution—PPLL

PPLL = PDC4 + PAC13 *FCLKOUT

FCLKOUT is the output clock frequency.

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:

•

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

= 50%

–

Bit 2

= 25%

–…

–

Bit 7 (MSB) = 0.78125%

–

Average toggle rate = (100% + 50% + 25% + 12.5% + . . . + 0.78125%) / 8

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%.

The PLL dynamic contribution depends on the input clock frequency, the number of output clock signals generated by the

PLL, and the frequency of each output clock. If a PLL is used to generate more than one output clock, include each output

clock in the formula by adding its corresponding contribution (PAC14 * FCLKOUT product) to the total PLL contribution.

Table 2-16 • Toggle Rate Guidelines Recommended for Power Calculation

Component

Definition

Guideline

Toggle rate of VersaTile outputs

10%

I/O buffer toggle rate

10%

Table 2-17 • Enable Rate Guidelines Recommended for Power Calculation

Component

Definition

Guideline

I/O output buffer enable rate

100%

RAM enable rate for read operations

12.5%

RAM enable rate for write operations

12.5%

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