LAB-XUSB Experimenter Board help

[Scampy]

check out the fuses, PLL etc. 48Hhz is needed for USB

But how would you get the timing right with a 20mhz crystal. I thought HS setting means that you run at the crystal speed, and the HS_PLL is typically a multiplier (of 4). IE to get 48 Mhz a 12 Mhz crystal is required, OSC is set to 48 and the fuse set to HS_PLL. - From the pictures of this LAB it's not clear if you can interchange the crystals, which is why I found that confusing.

[Tabsoft]

Malc,

ERMEGM is not using a 18F4550 in the board. He is using a 16F874A.
It's max rate is 20MHz using HS mode.

The 18F4550 is a bit of a different animal as far as I can tell looking at the DS.

It can take a 20MHz input in HSPLL mode that then gets divided by 5 to drive a 4MHz input into the PLL to get a 96MHz PLL clock. You can then select to divided down to 48MHz for the MCU clock. This allows the USB and MCU to run from a common source but at different rates.

[Scampy]

Malc,

ERMEGM is not using a 18F4550 in the board. He is using a 16F874A.
It's max rate is 20MHz using HS mode.

The 18F4550 is a bit of a different animal as far as I can tell looking at the DS.

It can take a 20MHz input in HSPLL mode that then gets divided by 5 to drive a 4MHz input into the PLL to get a 96MHz PLL clock. You can then select to divided down to 48MHz for the MCU clock. This allows the USB and MCU to run from a common source but at different rates.

Thanks for the explanation... learning something new every day

[Tabsoft]

For me too.
Had to take a look at the 4550 DS to get an understanding of it.

[ERMEGM]

Thank you for the insight.

Tony