problem with j-link

[alberto110]

Hi,
I have problem with Jlink and lpc1768 , when using intenel RC osc it work fine but doesn't work with externel crystal .
after inserting crystal to pcb , jlink does'nt find lpc1768 anymore .

[alberto110]

ok .there is a problem with oscillator . it  doesn't oscillate .

http://imgur.com/zpREy

[Old_but_Alive]

just a couple of things.
1. there seems to be a short stub on C15. should it be there, or should it be a track to connect gnd.
2. very bad practice to have any signal tracks near to the xtal circuitry.
I always surround the xtal and its 2 capacitors with a gnd track.
you seem to have a signal track between the 2 caps C15 and C16 - bad news !!!!

check that the gnd is actually connected to C15/C16 gnd

it looks like an Altium design.
can you post a link to your files, or send me a PM, then I will have a look at them.

[zab]

  The wire next to crystal is make more than half circle and passing through C15 C16 will definitely have /create interference.  In hi frequency induction heating, applicator coil is made in this way (Ohm like sign ie. half circle) for transfer of power from generator to work piece. What you need is add a simple jumper for this wire . this suggestion is for PCB design.

[alberto110]

I remove track between caps and short track after cap  . but not make PCB already .
i hear that rotating the crystal 90 degree and hence make different length of track between crystal and uc may solve problem .

[Old_but_Alive]

no, the  crystal is in a good place.
get rid of the signal track which runs under the capacitors.
Also, you need a ground plane on the other side of the board, so its under the xtal/capacitors, and acting as a ground shield.
This looks like a 2 layer board, so you must flood the bottom layer with as much ground plane as possible

[alberto110]

as Old_but_Alive told , board changed
blue plane in bottom layer is GND
http://i.imgur.com/rCIHD.jpg?1


so the track of Xtal1 and Xtal2 could be equal ?

[Old_but_Alive]

thats the way I would have done it, the tracks dont need to be equal, but thats ok.

just dont route PO.27 and PO.28 inside that ground environment.

you could get P027 and P028 out of the chip with via's by reducing the gnd track that is close to P028 to let p028 free

also P1.30 and P1.31 will now need to be routed under the chip , and out thru vias.

the absolute rule with xtal oscillators is NO SIGNAL TRACKS CLOSE OR UNDER XTAL CIRCUITRY

[Ichan]

ok .there is a problem with oscillator . it  doesn't oscillate .

Have you check for the proper LPC oscillator configuration? I think there is at least two range can be selected, and before switching to the main osc in software it is better to check the main oscillator status, ready or not.

-ichan

[alberto110]

Have you check for the proper LPC oscillator configuration? I think there is at least two range can be selected, and before switching to the main osc in software it is better to check the main oscillator status, ready or not.

-ichan

in the program ( generated automatically by keil  ) there is line the wait for main oscillator to be stable .
my software stop at this line .

[zab]

Please consult UM10360 LPC17xx User manual. The manual has detail of setting main osc.
see the link http://www.nxp.com/documents/user_manual/UM10360.pdf

at page 28
3.7.1 System Controls and Status register give you the value of the register for Keil.

OSCRANGE  Main oscillator range select. R/W 0

0 The frequency range of the main oscillator is 1 MHz to 20 MHz.
1 The frequency range of the main oscillator is 15 MHz to 25 MHz.

  OSCEN    Main oscillator enable. R/W 0

0 The main oscillator is disabled.
1 The main oscillator is enabled, and will start up if the correct external circuitry is connected to the
    XTAL1 and XTAL2 pins.

 OSCSTAT
   Main oscillator status. RO 0
0 The main oscillator is not ready to be used as a clock source.
1 The main oscillator is ready to be used as a clock source. The main oscillator must be enabled via the
    OSCEN bit.

at page 31
4.3.2 Main oscillator
Here you can see the components required for main oscillator.

[alberto110]

i used system_LPC17xx.c  that has a configuration page so we can choose options by mouse click  and no need of setting registers directly .
all setting are ok like zab post (i think ) .

also , is this better arrangement ?

http://imgur.com/jpLK8

[zab]

  Please share the code and circuit .perhaps then I would be able check it myself.so that problem can be traced out. circuit of crystal looks ok.
My suggestion is to use simple code.simple configuration without PLL. just to see hardware is ok. then goto original task.