Using a 18F4550 instead of 18F452

OE8PCK · Joined: 19 Apr 2009 Posts: 14 Location: Klagenfurt, AUSTRIA

Firstly I don't really know if this is a problem that can be EASILY solved on a forum.
I will explain what I want to do and then see if anyone is willing to look into it and what information they need.
The program , which runs completely well on a 18F452 is design to read voltages which come from a HF receiver and then display them on an 16x2 LCD. There is also a menu system which can be accessed using a function button and three other button which are placed under the LCD and are used to change the display and also calibrate the program. Smile

Now I have changed the program by changing the PIC from 18f452 to 18f4550 and adding NOXINST to the fuses. The code compiles successfully and I then programmed the chip. Now the chip runs, but when I try to push the function button no display is shown on the LCD. Sad

I do not even know where to start looking since I am complete beginner. Embarassed

I want to use the 4550 because of the USB function that I intend to include in the program.
The program is very big (1143 lines, plus smaller subprograms) and therefore unsuitable for the message body so I would have to send it in another way if anybody responds.
If this is not something for a forum please tell me and I am sorry. Rolling Eyes

Regards, Paul OE8PCK

Regards,
Paul OE8PCK

Ttelmah · Guest

The first thing to look at, is 'what pins are being used'.
The 4550, doesn't have a port C3 pin, since the connection for this, is used for the USB voltage regulator. If the existing hardware, has a connection to pin 18, then it is not going to work on a 4550, without hardware changes.
If there is no connection to this pin, then it probably can be made to work (though bng able to use USB, will also require pins 23, and pins 24, to not be currently 'in use'). The other things that are likely to need changes, are some of the initialisation fuses. In particluar, the settings for peripherals that can be switched to other pins (like CCP1), and the extra ADC pins.
You need to work out what pins are actually being used on the 452, and what peripherals. You then have a chance of making the conversion...

Best Wishes

OE8PCK · Joined: 19 Apr 2009 Posts: 14 Location: Klagenfurt, AUSTRIA

Thanks very much for the useful information. All is now clear. The pins you mentioned are all used with the software, changing them would be like writing everything new. Sad

You have really helped me not to run the wrong way. Very Happy

Regards Paul OE8PCK

libor · Joined: 14 Dec 2004 Posts: 288 Location: Hungary