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sadlpx
Joined: 19 Feb 2004
Posts: 23
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| Reading Chinese Scales output |
 Posted: Fri Sep 30, 2005 2:12 pm |
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I'm trying to read the output from some chinese calipers. The output stream is 2 - 24bit words back to back (total time about <1 ms), repeating at 50hz or every 20ms. Signal clock starts out with a 15-19 ms low then high for 55us, 24 bit word, high 110us, 24 bit word, high 55us then low for 15-19ms, repeat. Reading seems simple just a shift in routine reading on the falling edge. My problem is I'm having trouble filtering to the first falling edge. how could i set up to use the long (19ms) low to start my read cycle.
More data and scope images on the scales electronics are at this link.
http://www.shumatech.com/support/chinese_scales.htm
As always thanks in advance.
Last edited by sadlpx on Sat Oct 01, 2005 6:12 am; edited 1 time in total |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Re: Reading Chinese Scales output |
| Posted: Fri Sep 30, 2005 10:13 pm |
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| sadlpx wrote: | I'm trying to read the output from some chinese calipers. The output stream is 2 - 24bit words back to back (total time about 1 ms), repeating at 50hz or every 20ms. Signal clock starts out with a 15-19 ms low then high for 55ms, 24 bit word, high 110ms, 24 bit word, high 55ms then low for 15-19ms, repeat. Reading seems simple just a shift in routine reading on the falling edge. My problem is I'm having trouble filtering to the first falling edge. how could i set up to use the long (19ms) low to start my read cycle.
More data and scope images on the scales electronics are at this link.
http://www.shumatech.com/support/chinese_scales.htm
As always thanks in advance. |
You might want to edit your post and correct the timings because they are very confusing. You have used ms for all timings but most of the timings are in microseconds not milliseconds.
From the link you have published there is a long time between readings during which time the clock is held high. I would start by detecting this idle condition specifically detect the clock is high and remains high for 10ms. Once you have found this condition now wait for the clock to go low (possible start condition) validate the clock is still low after about 1/2 of the estimated low pulse width. Here you have found a valid start condition and the rest is up to you :-)
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Regards, Andrew
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