Figure 16-4illustrates the sources that create memory access time delays.

clock period shortening due to spectrum spreader

clock

address

clock to address output

data out

memory access time

data in setup time

output enable (early)

memory output enable time

Figure 16-4. Sources of Memory Access Time Delays

The gross memory access time is 2T, where T is the clock period. To calculate the actual memory access time, subtract the clock to address output time, the data in setup time, and the clock period shortening due to the clock spectrum spreader from 2T.

Example

clock = 29.49 MHz,

T = 34 ns,

operating voltage is 3.3 V,

bus loading is 60 pF,

address to output time = 8 ns (see Table 16-2),

data setup time = 1 ns,

the spectrum spreader is on in normal mode, resulting in a loss of 3 ns. The access time is given by

access time = 2T - (clock to address) - (data setup) - (spreader delay)

=68 ns - 8 ns - 1 ns - 3 ns

=56 ns

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Rabbit 3000 Microprocessor

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Jameco Electronics 2000, 3000 manual Example