Nova Electronics MCX514, Руководство пользователя

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NOVA electronics Inc. MCX514 -
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－ 33 －
2.2.6 Pulse Width and Speed Accuracy
■
Duty Ratio of Drive Pulse
The period time of
＋
/
－
direction pulse driving is decided by system clock SCLK. The tolerance is within
± １
CLK (For
CLK=16MHz, the tolerance is
±
62.5nsec). Basically, the duty ratio of each pulse is 50% as shown below. When the parameter
setting is DV = 1000pps, the driving pulse is 500
μ
sec on its Hi level and 500
μ
sec on its Low level and the period is 1.00 msec.
500 μ sec
1.00 msec
500 μ sec
SV = 1000
DV = 1000
Fig. 2.2-16 High/Low Level Width of Driving Pulse Output (1000pps)
In acceleration / deceleration driving, the Low level pulse length is shorter than that of Hi level pulse during the acceleration; the
Low level pulse is longer than that of Hi level pulse during the deceleration.
Constant Speed Area
Acceleration Area
Deceleration Area
tLA
tHA
tHC
tLC
tHD
tLD
tHA ＞ tLA
tHC = tLC
tHD ＜ tLD
Fig. 2.2-17 Comparison of Drive Pulse Length in Acceleration / Deceleration
■
The Accuracy of Drive Speed
The circuits to generate drive pulses on MCX514 operate with input clock (CLK). If CLK input is standard 16MHz, the user had
better drive the pulse speed in an exact multiple of CLK period (62.5nsec). However, in this case the frequency (speed) of driving
pulse can only be generated by an exact multiple of CLK. For instance, double
：
8.000 MHz, triple
：
5.333 MHz, quadruple
：
4.000
MHz, five times
：
3.200 MHz, six times
：
2.667 MHz, seven times
：
2.286 MHz, eight times
：
2.000 MHz, nine times
：
1.778 MHz,
10 times
：
1.600 MHz, ······. Any fractional frequencies cannot be output. Therefore, MCX514 uses the following method to output
any drive speed.
For instance, in the case of the drive speed DV = 980kpps, since this period is not an integral multiple of CLK period, pulses of
980kpps cannot be output under a uniform frequency. Therefore, as shown in the figure below, MCX514 combines 16 times and
17 times of CLK period in a rate of 674:326 to generate an average 980kpps.
16 16
16
17 16
16 17
Fig. 2.2-18 The Driving Pulse of 980kpps
According to this method, MCX514 can generate a constant speed driving pulse in a very high accuracy. And speed accuracy of
pulse output is ± 0.1% or less.
Using oscilloscope for observing the driving pulse, we can find the jitter about 1CLK (62.5nsec). This is no matter when putting
the driving to a motor because the jitter will be absorbed by the inertia of motor system.