6.25 Mhz crystal

David Betz

I know that a 6.25 MHz crystal is often used with the P1 for circuits intended to generate video. I have a number of these crystals that I bought from Parallax ages ago along with P1 chips. I now have a need for a 6.25 MHz crystal for another project but the BOM for that project calls for a 6.25 MHz 30pF capacitor. The Parallax store doesn't list a capacitance for the crystals they sell. Does anyone know if a Parallax supplied crystal is 30 pF?

evanh

The 6.25 MHz figure was just get a tidy 100 MHz. About as high as you'd want to push the Prop1. I went for 6 * 16 = 96 MHz in my Prop1 project. 6 MHz is common as mud and comes in cheap miniature oscillator module packages.

PS: I took one look at existing sysclock setup code and decided to make my own.

CON
' Custom PCB: 6 MHz SMD oscillator module
        CLKFRQ = 96_000_000
        OSCSEL = 0    ' 0 = XIN only,  1 = 4..16 MHz crystal,  2 = 8..32 MHz crystal,  3 = 20..60 MHz crystal
        CLKSEL = 7    ' 0=RCFAST  1=RCSLOW  2=XIN  3=PLL1X  4=PLL2X  5=PLL4X  6=PLL8X  7=PLL16X


PUB  main

    clkset( (CLKSEL>1)&32 | OSCSEL<<3 | (CLKSEL>2)&64, 13_000_000 )    ' config PLL but stay in RCFAST
    waitcnt(clkfreq>>6 + cnt)               'Wait 1/64 second for OSC/PLL stable
    clkset( (CLKSEL>1)&32 | OSCSEL<<3 | (CLKSEL>2)&64 | CLKSEL, CLKFRQ )    ' PLL switch over

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