Cant get right oscillator

[Gabriel]

HI all,

I cant get this to run at 20MHz with the external crystal.

I see on my scope that the crystal is oscillating but the pic is not running,

I can get it to run with the internal osc at 8MHZ but not the crystal.

[PCM programmer]

I compiled this for vs. 5.021. But anyway, look at the fuses at the end
of the .LST file. Look for anything weird or unintended:

[Gabriel]

you are right as usual.

Thanks!

G.
_________________
CCS PCM 5.078 & CCS PCH 5.093

[Ttelmah]

The key is that 'fuses' in general all set to '1', unless you change them.

On most older chips, the oscillator fuses had 'HS', or 'HS with PLL' setting, with the former turning the PLL off, so 'HS' also implied that the PLL was off.

On these particular chips, the PLL is a separate fuse, so selecting 'HS' does not automatically turn it off Instead there is a separate 'PLL on', or 'PLL off, but can still be software enabled' option. The default ('1') is the first.....

PCM_programmer points out a really 'critical' thing here. If you are having problems, look at the fuses at the end of the listing file. Do these agree with what you expect?. If not, what controls the bit that is different? (in this case, PLL_SW).

Fun isn't it!...

[temtronic]

Fun ..??? I've been down that road a couple of times!
I now take NOTHING for granted and configure every fuse on each own line.When I get the '1 Hz LED' program running right, I save the fuses as an 'include' file usually named 'pictype.fuz'. it not only gives me a set of known working fuses, it reduces visual 'space' in the program and saves me retyping misspelled or dylsexic words.

I do the same with defining I/O pins.If not used 'NU' is prefix of the name.
#define NUB4 PIN_B4 //pin 37 not used
#define SIO_TX1 PIN_C6 //pin 23 //data to PC (debug)
Again, saved as an 'include' file, 'PICtype_projectname.pnz'
It quickly allows me to see what pins are used or available.


hth
jay

[Gabriel]

Hi All,

This is a new pic for me... first time dealing with PLL.
I believed HS would disable the PLL.

Temtronic, like you have a "standard" fuses bit of code.
But my PICs were never this sophisticated.

Why aren't the fuses listed and described individually on the datasheet? Like a summary, instead of all over the DS.... sigh.

I got it to run properly.. so thank you all.
_________________
CCS PCM 5.078 & CCS PCH 5.093

[temtronic]

Part of the problem is that CCS calls them 'fuses' and Microchip calls them 'configuration words'.
I'm pretty sure section 4- Device Configuration of the Datasheet will describe them all for you( I looked at the LF version of the DS).

Fuses comes from the 'good old days' when you actually blew a small fuse(really !) to configure cells within the chip.I don't know why CCS called them that...

I also don't know why PICs do NOT default to digital I/O on all pins instead of some of the peripherals being enabled.

Just two quirks we have to be aware of.


hth
Jay

[Ttelmah]

The first problem is 'evolution'.
The earlier PIC's had one oscillator, and one set of fuses configuring them.
When the first PLL was added, it was an extra 'line' in the list of oscillator 'type'.
Then When USB PIC's came along, things got more complex, with the PLL having a lot of programmable divisions, and the CPU and the USB operated from the same, or separate clocks.
Then we switch to the PIC24's, where you have oscillator 'setup', as a separate entity from the 'oscillator to use'.
Then newer PIC's switched to having the PLL configurable _after boot_ in the software. Makes sense (allows you to slow the PIC and save power, then switch it up to higher speeds when needed), but means the oscillator now has to separate from the PLL...
Unfortunately the same names are used for all the types of chips, which is why the data sheet is your friend.

On the name, CCS followed MicroChip. The early PIC data sheets called them fuses. The earliest PIC's, were OTP devices though.

On digital I/O, you don't want a pin selected as 'digital' (even as an input), if analog sources are connected to it. Hence the default to analog in many cases. Why some peripherals default to enabled, is only answerable by MicroChip....

Best Wishes

[jeremiah]