strange RS232 GND problem

[Wilksey]

If you look at table 2-3 it says 20mhz input = 20mhz uC clock, PLL Div5(100) CPU Div 0

 

[Wilksey]

basically you are getting 4MHZ MAX into the USB PLL (20/5) that gives 96mhz on the PLL output, then the USBDIV is 2, 96/2 = 48MHZ, using a 24x multiplier on the clock

 

[ghostman11]

thanks for that, i will hang on till next week when they arrive.

 

[Wilksey]

no probs, do you have ANY crystals laying around? You may be able to use them for your testing? If you have what are their values?

 

[ghostman11]

only crystals i can find left in my draws are 8 mhz looks like logan had wandered off with the others lol

 

[Wilksey]

You can work with 8mhz!

PLLDIV2LLDIV0 = 2(001)
put the OSC in HSPLL Mode.
Select either CPUDiv 2(00) = 48mhz, or CPUDIV3(01) = 32MHZ, CPUDiv4(10) = 24mhz, or finally CPUDiv6(11) = 16MHZ.

So, for High speed USB select 48MHZ, for low speed USB select 24MHz (as highlighted in bold in the datasheet).

HTH

Wilksey

 

[ghostman11]

hmmm thats interesting i need to sit and read the usb part of the sheet, probaly at the weekend i cant see me getting enough time before then, still sorting out this controller for the new tunnels i am getting board laying cable lol

 

[Wilksey]

Yes, the Microchip datasheets are more of a challenge than an information source, lol, I always find myself referring back and forth between code and datasheet, design and datasheet and hardware and datasheet, so many options!

Laying cable is a tedious task, did a stint at the Tamar Bridge / Saltash Tunnel laying fibre optic about 5 years ago, constantly on the OTDR meter, checking for reliability!

What type of controller are you building? Is this what you wanted the radio stuff for?

 

[ghostman11]

yeah we have a 3 year contract to breed a tiny segmented worm for a well known pharma company so weve had 4 new large poly tunnels installed, the enviroment is pretty strigent in requirment so ive had to make a controller because i couldnt get a off the shelf one that would do all i wanted, the RF stuff is so i can monitor the sensors from the office but i will leave the controll in the tunnel units, its a bit of a pain but where i have sited the tunnels i cant lay cable direct to the office without alot of hastle

ive only tried usb once and i didnt put much effort into it i just followed a tutorial and it didnt work lol

 

[Wilksey]

Sounds complicated, lol.
You could also consider (depends on distance) GSM or Bluetooth if conventional radio fails.

Don't forget to mount antennas on the outside of the buildings and run suitable (50R?) rated cable to the antenna connector for best performance.

 

[ghostman11]

GSM might be an idea, if i was going to actualy control from the office i would probaly spend more but its only for me to monitor as i spend alot of time office bound at the mo.

 

[Wilksey]

Also, you can use a type of masthead amplifier to boost the RF signal, and things like directional antennas etc, RF = Loadsa fun!

You could get it to monitor and control, like an "auto adjust" feature?