IEEE 802.15.4 subsystem
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IEEE 802.15.4 subsystem Git Source Tree
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| Source at commit ae1455cc7dadfaa494c792217d1e4a53efb2747e created 7 years 1 month ago. By Stefan Schmidt, atusb-eui64: print out set address with upper case characters in hex | |
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| 1 | Correct atusd clock voltage divider |
| 2 | |
| 3 | |
| 4 | According to section 9.6.3 of the data sheet, an external clock supplied |
| 5 | to the AT86RF230 has a minimum peak-to-peak voltage of 400 mV and a |
| 6 | maximum of only 500 mV. Furthermore, the signal must be DC-free. |
| 7 | |
| 8 | The voltage divider in the 20100903 and 20100908 designs is too sensitive |
| 9 | to interference and the PLL constantly unlocks, rendering the device |
| 10 | dysfunctional. |
| 11 | |
| 12 | A more robust divider circuit can be obtained with the following |
| 13 | replacements: C7 -> 0R, R3 -> 33 pF, R4 -> 220 pF. After reworking the |
| 14 | 20100908 boards, they no longer suffer PLL unlocks. |
| 15 | |
| 16 | A Qucs simulation of the circuit can be found in ../atusd/sim/cdiv.sim |
| 17 | |
| 18 | Frequency measurements yield the following results: |
| 19 | |
| 20 | Host Board Error Meas. accuracy |
| 21 | (f, ppm) (ppm, nom.) |
| 22 | ------- --------------- --------------- --------------- |
| 23 | Ben #2 20100908-A +2 99.7 |
| 24 | +1 99.6 |
| 25 | Ben #1 20100908-A +23 99.7 |
| 26 | +24 99.9 |
| 27 | Ben #1 20100908-B +24 99.4 |
| 28 | +24 99.7 |
| 29 | Ben #2 20100908-B +2 99.8 |
| 30 | +2 99.9 |
| 31 | |
| 32 | The Ben's 12 MHz crystal has a tolerance of +/- 30 ppm, which is better |
| 33 | than the +/- 40 ppm required by IEEE 802.15.4. |
| 34 | |
| 35 | What remains to be verified is whether this change causes interferences |
| 36 | that may affect transceiver performance and may also violate emission |
| 37 | regulations. |
| 38 | |
