31 Jul 2010 7:13:34
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 Acqura now have Philips microcontrollers available for sale. If you need P89C668, P89C669, LPC76x or LPC900 family devices, check out our low MOQ's
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Take a look at our new forums. If you have a question about the 8xC51, LPC900, or MX families (or any 8051-related query) then ask your question here.
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| User proodink has posted this comment in the Clock/Xtal Forum |
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| external crystal problem |
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I have a problem with a lpc935 processor running at 3,3 Volt with an external HC49 crystal of 3.6864 MHz (drive level < 0,5 mW). The problem is that the amplitude of the XTAL2 signal is very low (1,54 Volt top-top sine wave using 15 pF shunt capacitors) while you expect around 3,1 Volt. The processor doesn't run well then.
In Philips application note AN10289 I found that the internal impedance of the internal amplifier between XTAL1 and XTAL2 is about 2 kohm to 5 kohm which is (in my opinion) too low to drive the XTAL2 level to the VDD voltage.
Does this problem sound familiar to anybody?
When I use the internal RC oscillator or an external clock signal, everything works fines. Only the external crystal solution does not function. The FOSC2-FOSC0 setting was 001 = medium frequency crystal or resonator, 100 kHz to 4 MHz.
I tried different settings for the I/O ports of P3.0 and P3.1 (Xtal2 push-pull mode) but did showed no difference.
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| Click here to see the whole discussion thread. |
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XA-80 |
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Programming Adapter |
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