| ??? 05/06/10 19:36 Read: times |
#175764 - Oscillator frequency. Responding to: ???'s previous message |
Kiran V. Sutar said:
Many thanks for your reply.
My client is using AT89C52 with a 12MHz crystal, with 22pF capacitor on Pin 18 and 19 of the cpu. My query was regarding the values of those capacitors. 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. 2. Is there a test circuit schematic to test the crystal; because I am having some crystals that are faulty. But cannot return it back to supplier, because they were soldered. So even before soldering how do we test whether the frequency is 12MHz or 11.0592MHz. Most of the times the printing does not match the frequency. I am having a crystal marked as 30MHz, but gives only 12 MHz. (after testing on the Oscilloscope). It looks as if you have a serious problem with your supplier. If a part has 12.000MHz stamped on it, I would not expect it to oscillate at 11.059MHz! Crystals are designed for series, parallel or overtone operation. You will probably find they should all work on the fundamental frequency either in series or parallel resonant circuit. The frequency will alter by less than 0.1% between modes. You check the data sheet of the parts that you are buying. If your supplier gives you rubbish, you stop buying from him. And I would broadcast this information about your supplier throughout India. As Kai has explained, you can test your crystal parameters. And compare with the published specification. And get back to your supplier for a full and frank discussion. I have never used a AT89S8253. I have used many other Atmel devices with no oscillator problems. I would be surprised if they have got a different oscillator design to every other chip they manufacture. If they did, I would guess they would have corrected it in later revisions. The 8253 has been around for a few years. David. |
| 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 |