Ceramic resonators accuracy

[RGV250]

Hi,
I am looking at making a few serial displays for debugging using the really neat serial display code Les posted elsewhere on the forum.
I have quite a few 18F2550 that can only go to 8mhz with internal osc but have PLL and can go to 32mhz using 8mhz external clock.
I am trying to keep the board as simple as possible so an 8mhz ceramic resonator seems the way to go but wondered will they be accurate enough for higher baud rates around 115200?

Bob
 

[trastikata]

Hi RGV250,

18F2550 is an USB capable device, it can run at 48 MHz with any external crystal from 4 to 32 MHz multiple of 4. Simpler and better than a resonator. I've been using that device family for years, if you need help with the set-up, let me know.

Regards

[trastikata]

Correction, I forgot a divider of 8 is not available, so no 32 MHz input for 48 MHz Fosc.

The input crystal with applied divider should give 4 MHz to the PLL input for 48 MHz Fosc. Dividers of 1,2,3,4,5,6,10 and 12 are available.

[RGV250]

Thanks, they are way overkill for what I want to use them for but I have them so might as well use them. I have some 4mhz ceramic resonators from the 16C84 days.
For some reason I read that the 48mhz was only available for USB?

I will have a look at the settings in the pub in a minute so it is guaranteed not to work

Regards,
Bob

[trastikata]

48MHz Fosc is available to the CPU unit. As an example for the settings, I take 8 MHz input:

- 8 MHz input / 2 prescaller --> 4 MHz to the PLL input
- 96 MHz PLL output / 2 postscaller --> 48 MHz Fosc

[RGV250]

Thanks, so if I have ext 4mhz resonator and prescaler of 1 I should get 48 as well.

Bob

[trastikata]

Thanks, so if I have ext 4mhz resonator and prescaler of 1 I should get 48 as well.

Bob

Indeed.