C164CM datasheet(54/68 Pages) INFINEON

54 / 68 page

C164CM

C164SM

Data Sheet

V1.0, 2001-05

Due to this adaptation to the input clock the frequency of

fCPU is constantly adjusted so

it is locked to

fOSC. The slight variation causes a jitter of fCPU which also effects the

duration of individual TCLs.

The timings listed in the AC Characteristics that refer to TCLs therefore must be

calculated using the minimum TCL that is possible under the respective circumstances.

The actual minimum value for TCL depends on the jitter of the PLL. As the PLL is

constantly adjusting its output frequency so it corresponds to the applied input frequency

(crystal or oscillator) the relative deviation for periods of more than one TCL is lower than

for one single TCL (see formula and Figure 12).

For a period of

× TCL the minimum value is computed using the corresponding

deviation DN:

(

× TCL)min = N × TCLNOM - DN; DN [ns] = ±(13.3 + N × 6.3)/fCPU [MHz],

where

N = number of consecutive TCLs and 1

≤ N ≤ 40.

So for a period of 3 TCLs @ 25 MHz (i.e.

N = 3): D3 = (13.3 + 3 × 6.3)/25 = 1.288 ns,

and (3TCL)min = 3TCLNOM - 1.288 ns = 58.7 ns (@ fCPU = 25 MHz).

This is especially important for bus cycles using waitstates and e.g. for the operation of

timers, serial interfaces, etc. For all slower operations and longer periods (e.g. pulse train

generation or measurement, lower baudrates, etc.) the deviation caused by the PLL jitter

is neglectible.

Note: For all periods longer than 40 TCL the N = 40 value can be used (see Figure 12).

Figure 12

Approximated Maximum Accumulated PLL Jitter

MCD04455

Max. jitter

±1

±10

±20

±30

±26.5

110

This approximated formula is valid for

40 and 10 MHz

CPU

25 MHz.

10 MHz

16 MHz

20 MHz

25 MHz

–

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