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Clock options on the UAV2

Started this discussion. Last reply by William Premerlani Feb 2, 2009. 6 Replies 0 Likes

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William Premerlani replied to Thomas Roell's discussion 'Clock options on the UAV2'

On a related topic, Thomas thought that the source code for the PWM for my GentleNav firmware produced pulses that were 2-4 milliseconds wide instead of 1-2 milliseconds wide. The code is correct, the pulses are between 1-2 milliseconds wide. Here…

Feb 2, 2009

William Premerlani replied to Thomas Roell's discussion 'Clock options on the UAV2'

Thomas, I finally understand what you are getting at. You are concerned about aligning the data streams that are not sampled at the same time. I will give you the short answer and the long answer. First, the short answer. The short answer is that…

Feb 2, 2009

William Premerlani replied to Thomas Roell's discussion 'Clock options on the UAV2'

Thomas, I agree with you that with the 40 bit accumulator of the dsPIC30F4011, I will be able to avoid floating point. The math library furnished by Microchip includes some vector and matrix math routines that take full advantage of the PIC…

Feb 1, 2009

Thomas Roell replied to Thomas Roell's discussion 'Clock options on the UAV2'

Bill, Makes sence with the low load. If you add however more complex filtering that might change. IMHO with a 40bit ACC you may avoid floating point anyway. With the FRC I was surprised to see the 1PPS signal from the GPS not being connected. That…

Jan 30, 2009

William Premerlani replied to Thomas Roell's discussion 'Clock options on the UAV2'

Thomas, Here is a shorter answer. The FRC is precise enough. With PLL options, it can be set for 7.5, 30, 60, or 120MHz. The external 16MHz clock fills the gap between 7.5 and 30, so there is a choice of FOSC between 7.5 and 120MHz, with each…

Jan 30, 2009

William Premerlani replied to Thomas Roell's discussion 'Clock options on the UAV2'

Thomas, The two options of an external 16MHz crystal and the FRC were chosen to combine with the various PLL options to give a wide range of clock frequencies for several choices for balancing computational speed with power requirements. As I am…

Jan 30, 2009

Thomas Roell replied to Chris Anderson's discussion 'Discussion forum for Sparkfun 3-axis IMU-based autopilot board'

Jan 30, 2009

Clock options on the UAV2

Just out of curiousity, I do not quite follow the choice of the external 16MHz clock. In essence this means if you are using the HS setting in FOSC your CPU will be clocked with 4MHz (FCY == FOSC / 4). So your only real choice to get decent CPU performance is to use FRC w/PLL x16. In which case of course you'd loose the precision of having an external crystal.

Discussion posted by Thomas Roell Jan 30, 2009

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