| ??? 03/24/07 09:44 Read: times |
#135752 - AT89S8253 clocking problem |
Hi I have just completed manufacturing 1000 PCB's using the AT89S8253-24AU processors. The crystals run at 22.1184Mhz and are loaded with 5.6pf caps. The problem I have is that about 25% of the boards will not start their crystal oscillators correctly. In fact they start at a slower speed (always at about 1/4 of the normal) and stay like this for a while. Some will clock up and continue normally. When the processor is changed the problem is almost always resolved. We did have one that needed to CPU to be changed twice. PLEASE can you help me to determine the cause of this problem. I have never seen this before but normally used the AT89S8252 version. Is this a cap loading problem? Is it possible the processors are faulty? When I connect a scope to the XTAL1 the system ramps up to speed immediately. XTAL2 is not giving a good signal at all. Kind regards Alex
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| Topic | Author | Date |
| AT89S8253 clocking problem | 01/01/70 00:00 | |
| The scope probe is the clue!! | 01/01/70 00:00 | |
| The tale of a 1000 fingers | 01/01/70 00:00 | |
| Alex did what the datasheet demands | 01/01/70 00:00 | |
| 1M across cap | 01/01/70 00:00 | |
| are you sure it is not 1/3? | 01/01/70 00:00 | |
| I had the same problem | 01/01/70 00:00 | |
| Works!! But is it a solution | 01/01/70 00:00 | |
| is it 1/4 or 1/3 | 01/01/70 00:00 | |
| Speed unstable | 01/01/70 00:00 | |
| May be clock amplitude... | 01/01/70 00:00 | |
| Crystal frequency | 01/01/70 00:00 | |
| An interesting article... | 01/01/70 00:00 | |
| Use an external oscillator! | 01/01/70 00:00 | |
wait a year or more for the errata | 01/01/70 00:00 |