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Microchip recommends add 100 nF capacitor between Vdd and Vss power inputs of the PIC18F24J50 or PIC18F26J50 microcontroller. Though the chip works perfectly with 4 MHz crystal even without it, the microcontroller would often fail when it runs on higher frequencies. See the circuit for a 12 MHz application on the schematic on the righthand side.
There are minor changes according to the basic circuit. Different crystal capacitors (22 pF instead of 27 pF) and a 100 nF ceramic capacitor (with a resonance frequency in the range of 200 MHz or higher) were used. Firmware packs are available from Downloads section in PIC18F2xJ50 firmware vx.y - all subversions.ZIP files (example: PIC18F24J50 firmware v2.6.4 - all subversions.zip6. DOWNLOADS), which contain general use versions as well as adapter versions of *.HEX files.
PIC18F24J50 microcontroller can run at variety of clock speeds. However, communication via USB requires precise timing and use of crystal resonator. The crystal resonator must provide frequency that is a multiple of 4 MHz. There are also some other requirements, so clock frequencies that allow proper USB operation are: 4, 8, 12, 16, 20, 24, 40 and 48 MHz. The external part of PIC18F2xJ50 oscillator circuit consists of two ceramic capacitors and a resonator. The Microchip recommended values for the capacitors are the following:
Click on the schematic to enlarge it.
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