| ??? 05/06/10 13:37 Read: times Msg Score: +1 +1 Informative |
#175750 - Equivalent series resistance is the critical parameter Responding to: ???'s previous message |
Kiran said:
My client is using AT89C52 with a 12MHz crystal, with 22pF capacitor on Pin 18 and 19 of the cpu. Usually 33pF caps should be used, in combination with fundamental quartzes. At higher frequencies you can go to 27pF and then to 22pF. But even then 33pF works beautifully. Kiran said:
1. How do we know the what is the value of the capacitor to be connected on Pin 18,19 of CPU, so that even if we change the CPU, the crystal (12MHz, or 24MHz) works. Have a look into the datasheet. Everything should be explained there. If not, contact the manufacturer. Kiran said:
2. Is there a test circuit schematic to test the crystal; because I am having some crystals that are faulty. The critical parameter of a quartz is its equivalent series resistance. This parameter decides whether the Pierce oscillator will start up at all, how stable the oscillation is and if the oscillator can run also at the extrem temperature ranges. The equivalent series resistance must be low! You will find low resistances in quartzes of good manufacturers. Also, the resistance is the lower the bigger the quartz is!!! So, one remedy for you could be to take the good old HC-49/U instead of a smaller one. Avoid SMD quartzes. There are circuits, which can be used to identify critical quartzes. They look a bit like the one shown by Arun. I can search in my archive if you like. Kai Klaas |
| Topic | Author | Date |
| Capacitor Value of MCS51 for Crystal | 01/01/70 00:00 | |
| What frequency? Fundamental or overtone? | 01/01/70 00:00 | |
| Reply to Kai Klass | 01/01/70 00:00 | |
| Equivalent series resistance is the critical parameter | 01/01/70 00:00 | |
| WHY? | 01/01/70 00:00 | |
| Of course!! | 01/01/70 00:00 | |
| Thanks to Erik, Kai and others | 01/01/70 00:00 | |
| Presumably because | 01/01/70 00:00 | |
| Oscillator frequency. | 01/01/70 00:00 | |
| Why not having a look into the datasheet? | 01/01/70 00:00 | |
| Thanks David Prentice | 01/01/70 00:00 | |
Your setup should include the micro... | 01/01/70 00:00 | |
| i had this problem before | 01/01/70 00:00 | |
| Reply to Arun Kumar | 01/01/70 00:00 | |
| may be this will help | 01/01/70 00:00 | |
| not necessarily | 01/01/70 00:00 | |
| Thanks Arun Kumar | 01/01/70 00:00 | |
| danger, danger | 01/01/70 00:00 | |
| Only the AT89S8253 is problematic! | 01/01/70 00:00 | |
| clarification appreciated | 01/01/70 00:00 | |
| I only recall the ones... | 01/01/70 00:00 | |
| with no interest ... | 01/01/70 00:00 | |
| Erik, you hurt me... | 01/01/70 00:00 | |
| no hurt intended | 01/01/70 00:00 |