4550 osc

[MyBuddy]

I'm a bit new with this chip and I'm having problems with the oscillator settings. Basically, I already have a program and circuit working with the chip and a 4MHz XT.

The problem is that when I replace the crystal with a 20MHZ HS nothing communicates anymore. Debug and SPI, to be exact.

I've changed my DEFINE OSC to 20 and made sure the right MHz and Type are selected in melabs programmer. Is there something else I am missing to get the serial ports back to normal speed?

I'm using MicroCode Studio - PicBasic Pro with the MeLabs USB Programmer.

[Macgman2000]

First we need some info....What chip body? What compiler version? Is it a 20Mhz crystal or resonator?

Nick

[MyBuddy]

18f4550 is the chip, 40 pin dip. I'm using PicBasic Pro 2.46. And it's a quartz crystal.

[comwarrior]

have you put capacitors between the oscilator pins and ground?

[MyBuddy]

Yes, did that. 22pF

Reset is high, too.

[comwarrior]

ok, cool, thaught i'd ask a stupid question...

i used the 18F4550 myself and i also use the same OSC so, i'll run through my settings, however, i'm using winpic800 with a JDM programmer...

OSC: HS oscillator, PLL enabled, HS used by USB
CPU system clock: 96MHz PLL dev 5
Oscilator selection: Devide by 5 (20MHz input)
Vbor: 2.7V
Brown-out restet: Enabled in hardware only
Watchdog: 1:32768
FCMEM enabled
IESO enabled
WDTEN enabled
PWRTEN disabled
CCP2MX enabled
PBADEN enabled
LPT1OSC enabled
MCLRE disabled
DEBUG disabled
STVREN enabled
LVP enabled
ICPORT enabled
XINST enabled
USBPLL enabled
VREGEN enabled

All CP's are disabled
All EBT's disabled
All WRT's disabled

Acording to oshonsoft's pic18 simulator IDE the BASIC code for those options are asfollows...

Define CONFIG1L = 0x3C
Define CONFIG1H = 0xCE
Define CONFIG2L = 0x17
Define CONFIG2H = 0x1F
Define CONFIG3L = 0x00
Define CONFIG3H = 0x07
Define CONFIG4L = 0xE1
Define CONFIG4H = 0x00
Define CONFIG5L = 0x0F
Define CONFIG5H = 0xC0
Define CONFIG6L = 0x0F
Define CONFIG6H = 0xE0
Define CONFIG7L = 0x0F
Define CONFIG7H = 0x40

Hopefully, some of that will help...
if not, can you post a screen shot of your programmers config options screen?

Thanks

[b1arrk5]

The '4550 supports USB, and the oscillator section has a lot of options. Try the following;
asm
__CONFIG _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L

__CONFIG _CONFIG1H, _FOSC_HSPLL_HS_1H & _FCMEN_OFF_1H & _IESO_OFF_1H

__CONFIG _CONFIG2L, _PWRT_ON_2L & _BOR_ON_2L & _BORV_2_2L & _VREGEN_ON_2L
__CONFIG _CONFIG2H, _WDT_OFF_2H
__CONFIG _CONFIG3H, _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H & _CCP2MX_ON_3H
__CONFIG _CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _ICPRT_OFF_4L & _XINST_OFF_4L & _DEBUG_OFF_4L
endasm
define OSC 48 'core running at 48Mhz
DEFINE DEBUG_REG PORTA 'pin Porta.5 serial out to debug
DEFINE DEBUG_BIT 5
DEFINE DEBEG_BAUD 2400
DEFINE DEBUG_MODE 0 '0 = TRUE, 1 = INVERTED

This setup works with a 20 Mhz crystal. You will also find more information if you do a search here for 18f4550

Good Luck,
Jerry