SX48 external clock source problems

popr8084

I purchased a SX48 protoboard and an SX-Key. For the life of me I cannot get my program in SX/B to run on any external crystals of resonators. It works with the internal clock, and with the clock produced by the SX-Key though.

Has anyone else had this problem?

PJAllen

You're·probably not·specifying the correct oscillator type in the Device directive.

Sasha

I agree with PJ Allen...Tray something like:

DEVICE SX28, OSCXT2, TURBO, STACKX, OPTIONX 
FREQ 20_000_000

More about this you can find in "SX FAQ2" on page 19.

DEVICE | FOSC2..0 | Meaning

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OSCLP1 000 low power crystal (32 kHz)
OSCLP2 001 low power crystal/resonator (32 kHz to 1 MHz)
OSCXT1 010 normal crystal/resonator (32 to 1 MHz)
OSCXT2 011 normal crystal/resonator (1 MHz to 24 MHz)
OSCHS1 100 high speed crystal/resonator (1 MHz to 50 MHz)
OSCHS2 101 high speed crystal/resonator (1 MHz to 50 MHz)
OSCHS3 110 high speed crystal/resonator (1 MHz to 75 MHz)

Regards

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Think deep......Dive shallow !!!

popr8084

I dont have a problem using my SX-Tech board with either oscillator. But when I switch over to the SX-48 Proto Board I cant get it to work...

PJAllen

OK, in your first post your referred to "external crystals of resonators" (sic) and in your reply you referred to "either oscillator."· Are you using crystals, resonators, or external oscillators?· It makes a difference.

If you're using an appropriate DEVICE directive (DEVICE SX48, OSC...) then maybe you have a bad board.

On the Protoboards, there is a socket for the resonator, X2; the crystal gets plugged into X1/Cx·on the Protoboards (the crystal leads get placed into the outside terminals.)


Post Edit -- http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/SX48-52ProtoBDRevBSchematic.pdf

Post Edited (PJ Allen) : 11/8/2008 3:10:05 PM GMT

popr8084

I am using the resonators that came with the sx-tech board kit. I tested a quick program on another sx-48 proto board that I had laying around and it worked with the resonator. but when i replicate the same thing with the other board I get nothing. I checked all of the connectors for the resonator sockets and they are all connected properly on both boards. I would say that maybe somthing is wrong with the actual chip, but why would it work when the SX-key is acting as the clock?

these are the settings I used on the other board when it worked:

DEVICE SX48, OSCHS3
FREQ 50_000_000

PJAllen

The SX-Key provides the clock when it's plugged in (and till it's removed.)

If one works and one doesn't, otherwise "same same",·then it looks like a bad board.· Get in there with a magnifier and have a look-see.· If possible, see if you have continuity between the IC pins and the corresponding resonator socket pins.· May be that there's a bad solder joint or some other manufacturing defect.·

popr8084

I checked the continuity between the resonator socket and the two oscillator pins for the programmer, and they are connected. I also checked to the chip itself and they are connected as well...

I am so confused... this makes no sense.

PJAllen

Well, if you have continuity from the sockets [noparse][[/noparse]emphasis -·with ohmmeter probe in the socket] to·the IC pins and you have a good ground (Vss) to the center socket, X2, too, then that's a head-scratcher for sure.

Something else I'd try is soldering some straight wire on one of those resonators or work out a little adapter board·so that I could plug·one into X1 or Cx (just for grits and grins.)· Any other suggestions would likely void your warranty, so I won't mention them.

I guess you could print out this thread and send it along with the protoboard for an In Warranty exhange (RMA.)

popr8084

tried it with no luck.

i'm not exactly sure how they work but does the chip have to trigger the resonator to oscillate? maybe something is wrong with the chip itself?

Do the 75MHZ TTL crystals oscillate by themselves? I wish I had one to try before I buy them...

I would hate to have to replace the board. I already have things soldered onto it...

popr8084

I hooked up a simple RC oscillator and it worked. So for some reason it OSC2 pin does not work...

Dick Whipple

I've had problems with the Proto 48 resonator, but found that a 1 M Ohm resistor across it does wonders.· I don't have a 100 MHz scope to see what's happening, but it made all the difference.· Hope this helps.

Macgman2000

How does one know whether or not the resistor is needed? I wrote a simple PWM routine to test my new SX48 boards. They both work at 20Mhz, works at 50Mhz too but dang do the chips get toasty! Under what circumstances do these boards not work without the resistor?

Nick

Dick Whipple

I couldn't make a simple LED blinker work at 50 MHz without the resistor.· See attached code.· Obviously the small load presented by the resistor dampens the oscillation and maybe takes sharp edges off.· I can't see that it would hurt, but if you don't need it, don't use it.

dkemppai

Dick Whipple said...
I've had problems with the Proto 48 resonator, but found that a 1 M Ohm resistor across it does wonders.· I don't have a 100 MHz scope to see what's happening, but it made all the difference.· Hope this helps.

Also, try add a 5pf cap from OSC2 to ground...

I've had a lot of trouble getting these SX48's to oscillate with a resonator. I use a 1M from OSC1 to OSC2, and a 5pF from OSC2 to ground. That seems to fix most of my·resonator issues...

-Dan


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"A saint-like quantity of patience is a help, if this is unavailable, a salty vocabulary works nearly as well." - A. S. Weaver