MC68340FE16E Datasheet, PDF (396/441 Pages) Freescale Semiconductor, Inc – Integrated Processor with DMA User’s Manual

Freescale Semiconductor, Inc.
CLKOUT
OUTPUT1
OUTPUT2
T/2
td1
t _d2
ts
Figure 10-13. Skew between Two Outputs
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.
MOTOROLA
MC68340 USER’S MANUAL
10-9
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