Motorola MC68340 User Manual

MOTOROLA

10-9

OUTPUT2

OUTPUT1

CLKOUT

T/2

td1

d2

t s

t

The method for calculating a frequency-adjusted ts is as follows:

ts' = ts + N (Tf'/2 – Tf/2) + (Tf'/2 –  td1)

where:

ts' = the frequency-adjusted skew

ts = the skew at full speed

N = the number of full one-half clock periods in ts, if any

Tf'/2 = one-half the new clock period

Tf/2 = one-half the clock period at full speed

td1 = the propagation time for the first output from the clock edge

The following calculation uses a 16.78-MHz port, specification 21, R/

W

 high to 

A S

asserted, at 8 MHz as an example:

ts = 15 ns minimum

N = 0

Tf'/2 = 125/2 = 62.5 ns

Tf/2 = 60/2 = 30 ns

td1 = 30 ns maximum

therefore:

ts' = 15 + 0(62.5 – 30) + (62.5 – 30) = 47.5 ns minimum

In this manner, new specifications for lower frequencies can be derived for an MC68340.

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Freescale Semiconductor, Inc.

For More Information On This Product,

   Go to: www.freescale.com

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