prod/doc/index.html |
68 | 68 | <DD>In this context, the actual process of soldering components to |
69 | 69 | the unpopulated PCB, and all related tasks providing an input to |
70 | 70 | 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. |
72 | 73 | </DL> |
73 | 74 | |
74 | 75 | |
... | ... | |
114 | 115 | |
115 | 116 | <H2>Fault analysis</H2> |
116 | 117 | |
117 | | <H3>Component orientation</H3> |
| 118 | <H3>Component placement and orientation</H3> |
| 119 | |
| 120 | <H3>Supply voltages</H3> |
| 121 | |
118 | 122 | <H3>Clock frequency</H3> |
119 | 123 | |
| 124 | The flawless performance of the crystal oscillator is crucial for |
| 125 | operation. Anomalies are easy to detect with even a low-cost oscilloscope |
| 126 | and pinpoint specific problems and help to select further analysis steps. |
| 127 | <P> |
| 128 | The crystal used in <B>atben</B> and <B>atusb</B> has a nominal tolerance |
| 129 | of +/- 15 ppm at 22-28 C. Low-cost oscilloscopes typically have a timing |
| 130 | accuracy of |
| 131 | +/- 100 ppm, which means that only major excursions can be detected by |
| 132 | measuring the clock output with such an instrument. Full-speed USB only |
| 133 | requires an accuracy of +/- 2500 ppm. |
| 134 | We can therefore consider all results within a range of +/- 1000 ppm as |
| 135 | sufficient, and perform more precise measurements by other means. This |
| 136 | applies 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 |
| 143 | can be enabled with the following command: |
| 144 | <PRE> |
| 145 | atrf-txrx -d net:ben -C 1 |
| 146 | </PRE> |
| 147 | This configures <B>atben</B> as a promiscuous receiver. The reception |
| 148 | of 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 | |
| 163 | The transceiver provides the clock for the microcontroller in <B>atusb</B>. |
| 164 | A clock signal is therefore always available. Immediately after reset, |
| 165 | the transceiver generates a 1 MHz clock. When the microcontrolled comes out |
| 166 | of reset, it raises the transceiver's clock output to 8 MHz and then |
| 167 | enables 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 | |
120 | 183 | <P> |
121 | 184 | <HR> |
122 | | Last update: 2011-05-17 <I>Werner Almesberger</I> |
| 185 | Last update: 2011-05-18 <I>Werner Almesberger</I> |
123 | 186 | <HR> |
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