HS PLL OSC mode

[poul holmoe thomsen]

I am using the 18F852 with the PCH 3.112 compiler. My problem is
that I cannot make the mcu run 40 MHz using the PLL mode with a 10 MHz Oscillator.

I have changed the fuse to PLL (H4), changed the use_delay to 40000000 and selected the HS with PLL option in the ICD 2 advanced box.

Nevertheless, my program runs 4 times SLOWER now! And the
seriel comms are broken.

Have you any suggestions?
Thanks in advance,

Poul
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This message was ported from CCS's old forum
Original Post ID: 8013

[R.J.Hamlett]

:=I am using the 18F852 with the PCH 3.112 compiler. My problem is
:=that I cannot make the mcu run 40 MHz using the PLL mode with a 10 MHz Oscillator.
:=
:=I have changed the fuse to PLL (H4), changed the use_delay to 40000000 and selected the HS with PLL option in the ICD 2 advanced box.
:=
:=Nevertheless, my program runs 4 times SLOWER now! And the
:=seriel comms are broken.
:=
:=Have you any suggestions?
:=Thanks in advance,
:=
:=Poul
Do a search back on this message board about this. The PLL, is quite tempermental, the commonest problem is that it will fail to run, and give 'odd' frequencies, if the crystal is being a little overdriven. I found I _had_ to have a series resistor in the crystal drive, to get it to work reliably. Also look at the 'oscillator design' notes on the MicroChip site. Though most of these are only dealing with the 'standard' modes (not the PLL mode), the comments are applicable in general.
Also check which revision silicon you have. Though this is not mentioned in the errata sheets, I had soem very early 18F452's, which were 'pre-production' examples, and the oscillator was an area that gave problems on these. You may have a similar problem.

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 8014