Code running 19 times slower than intended

[jellis00]

I finally found the problem thanks to rteo who advised that the 18F2550/4550 data sheet shows in one place that the external osc won't function with a supply voltage to the MCU of less than 4.2 volts. I had been running a supply voltage of 3.3 volts as a battery power conservation measure. I then experimented and discovered, rteo is partially correct.....my 18F2550 external osc circuit won't oscillate reliably until the supply voltage is at least 3.6 volts.
This discovery is going to make me change the design for this product to a 4.2 volt supply rail.

[mackrackit]

Maybe your crystal will not run at a voltage lower than 3.6, but the 4550 will operate with an external OSC of 4MHz at 3 volts. I typically run this chip at 3.3 with SD cards.

If you want to save power and run at a lower voltage get a three pin resonator at 4MHz.

[falingtrea]

If you want to be able to run at lower than 4.2 volts you should probably be using the LF version of the part. Looks like the LF version will work from 2V to 5V with slower clocks the lower the voltage goes. Some F parts may work lower than the 4.2V spec, but there may be some that flat out won't.

[Bruce]

Dave,

Are you sure you're not using the LF version running at 3V?

[mackrackit]

Yes, I just doubled checked, again.

Do not laugh at the messy board, everything on it runs at 3.3 volt. Another interesting thing is this chip can also be programmed at 3.3. I have the PicKit2 feeding a LM317. The PicKit is fooled into thinking it is running at 5 volts.
Along with the SD card there is a MAX6675 and a DS1337. Working on a PYRO LOGGER.

And the data sheet is a bit miss leading?
I take the extended range (LF) as going down to 2 volts.
I guess I could have a batch that was labeled incorrectly?

[Bruce]

Are you running it at 48MHz @ 3V?

[mackrackit]

Yup, with a 4MHz external purchased from you

DEFINE OSC 48
@ __CONFIG   _CONFIG1L, _PLLDIV_1_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@ __CONFIG   _CONFIG1H, _FOSC_HSPLL_HS_1H
@ __CONFIG    _CONFIG2H, _WDT_OFF_2H & _WDTPS_512_2H
@ __CONFIG    _CONFIG3H, _PBADEN_OFF_3H & _MCLRE_OFF_3H 
@ __CONFIG    _CONFIG4L, _LVP_OFF_4L & _ICPRT_OFF_4L &_XINST_OFF_4L