| ??? 01/31/06 23:33 Read: times |
#108845 - Table explained Responding to: ???'s previous message |
Steve M. Taylor said:
Trevor Jacobs said:
Just as a comparison I looked at the voltages of the oscillator with different cap values:
Crystal - 11.0592 MHz - Fundamental mode-AT-CUT - 18pF Cap value Voltage 0pF (no caps) 3.4 Vpp 5pF 2.9 Vpp 18pF (correct load)1.4 Vpp On the AT89S8252 - same PCB design: 18pF 4.4 Vpp 18pF - 24 MHz 4.0 Vpp The above 24 MHz crystal has the same specs as the 11.0592. The drive voltages from the AT89S8253 are quite low! Even with no caps. Not sure I understand the table Trevor, can you explain again ? Hi Steve, No worries. The first 3 entries on the table are the AT89S8253 on a PCB running with the listed values of capacitors from each crystal pin to ground. The voltage is the peak to peak reading that I measured with the caps installed. The voltage reading was taken with a Techtronix TDS3054 O-Scope off of the XTAL1 pin. The scope probe may effect the result slightly, so it's a relative measurement. The 4th and 5th entries in the table are of the XTAL1 pin on an AT89S8252. The first crystal (4th entry) is the same 11.0592 MHz one that I used on the AT89S8253, with the normal 18pF caps in place. The 5th entry is a 24 MHz crystal. Notice how much more drive you get with the correct loading on an 8252! Trev |
