Date:2011-05-18 12:23:11 (12 years 10 months ago)
Author:Werner Almesberger
Commit:e86997e94d83ad1a9936f8f7af13f488c39d28a8
Message:prod/doc/index.html: more fault analysis, mainly clock frequency

Files: prod/doc/index.html (2 diffs)

Change Details

prod/doc/index.html
6868  <DD>In this context, the actual process of soldering components to
6969    the unpopulated PCB, and all related tasks providing an input to
7070    this process. Such related tasks include the configuration of the
71    SMT line, and testing and conditioning of the components to solder.
71    SMT line, and testing and conditioning of the components prior to
72    soldering.
7273</DL>
7374
7475
...... 
114115
115116<H2>Fault analysis</H2>
116117
117<H3>Component orientation</H3>
118<H3>Component placement and orientation</H3>
119
120<H3>Supply voltages</H3>
121
118122<H3>Clock frequency</H3>
119123
124The flawless performance of the crystal oscillator is crucial for
125operation. Anomalies are easy to detect with even a low-cost oscilloscope
126and pinpoint specific problems and help to select further analysis steps.
127<P>
128The crystal used in <B>atben</B> and <B>atusb</B> has a nominal tolerance
129of +/- 15 ppm at 22-28 C. Low-cost oscilloscopes typically have a timing
130accuracy of
131+/- 100 ppm, which means that only major excursions can be detected by
132measuring the clock output with such an instrument. Full-speed USB only
133requires an accuracy of +/- 2500 ppm.
134We can therefore consider all results within a range of +/- 1000 ppm as
135sufficient, and perform more precise measurements by other means. This
136applies to <B>atben</B> as well as to <B>atusb</B>.
137<P>
138
139
140<H4>Measuring the clock on atben</H4>
141
142<B>atben</B> normally does not output a clock signal. A 1 MHz clock
143can be enabled with the following command:
144<PRE>
145atrf-txrx -d net:ben -C 1
146</PRE>
147This configures <B>atben</B> as a promiscuous receiver. The reception
148of any IEEE 802.15.4 frame or pressing Ctrl-C will terminate the command.
149<P>
150<TABLE>
151<TR><TH align="left">Clock<TH align="left">Action
152<TR><TD>0 Hz<TD>Check voltages; check that the clock is enabled;
153  check for shorts around crystal; check connectivity of crystal
154<TR><TD>0.999-1.001 MHz, ~3.3 Vpp<TD>Perform precision measurement with
155  <B>atrf-xtal</B>
156<TR><TD>Other<TD>Check voltages; check for contamination around crystal
157</TABLE>
158<P>
159
160
161<H4>Measuring the clock on atusb</H4>
162
163The transceiver provides the clock for the microcontroller in <B>atusb</B>.
164A clock signal is therefore always available. Immediately after reset,
165the transceiver generates a 1 MHz clock. When the microcontrolled comes out
166of reset, it raises the transceiver's clock output to 8 MHz and then
167enables USB.
168<P>
169<TABLE>
170<TR><TH align="left">Clock<TH align="left">Action
171<TR><TD>0 Hz<TD>Check voltages; check for shorts around crystal; check
172  connectivity of crystal
173<TR><TD>0.999-1.001 MHz, ~3.3 Vpp<TD>Check presence of firmware; check for
174  shorts on SPI signals; check connectivity of SPI signals
175<TR><TD>7.992-8.008 MHz, ~3.3 Vpp<TD>Perform precision measurement with
176  <B>atrf-xtal</B>
177<TR><TD>Other<TD>Check voltages; check for contamination around crystal
178</TABLE>
179
180
181<H4>Precision measurements</H4>
182
120183<P>
121184<HR>
122Last update: 2011-05-17&nbsp;&nbsp;<I>Werner Almesberger</I>
185Last update: 2011-05-18&nbsp;&nbsp;<I>Werner Almesberger</I>
123186<HR>
124187</BODY>
125188</HTML>

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