Motorola MC68340 manual Signal Width Specifications

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Additionally, the relationship between the asynchronous inputs and the clock edge, as shown in Figure 10-11, does not change as frequency changes.

A second type of specification indicates the minimum amount of time a signal will be asserted. This type of specification is illustrated in Figure 10-12.

T/2 N

CLKOUT

t d

OUTPUT

t w

Figure 10-12. Signal Width Specifications

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

tw' =wt + N (Tf'/2 – Tf/2) + (Tf'/2 –dt)

where:

tw' = the frequency-adjusted signal width

tw = the signal width at 16.78 MHz

N = the number of full one-half clock periods in tw

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

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

td = the propagation time from the clock edge

The following calculation uses a 16.78-MHz part, specification 14, AS width asserted, at

12.5MHz as an example: tw = 100 ns

N = 3

Tf'/2 = 80/2 = 40 ns

Tf/2 = 60/2 = 30 ns

td = 30 ns maximum

therefore:

tw' = 100 + 3(40 – 30) + (40 – 30) = 140 ns

The third type of specification used is a skew between two outputs (see Figure 10-13).

10-8MC68340 USER’S MANUALMOTOROLA

For More Information On This Product,

Go to: www.freescale.com