External clock not working on 18LF24k22

alen12 · Joined: 14 Mar 2014 Posts: 6

I am using 18LF24k22 and I get garbage on my serial rs232 but if I switch it to internal oscillator everything works ok. Anyone can help me here. I checked my hardware and everything looks ok. I replaced 22pf capacitors and also my 8MHZ crystal but no difference. I am using CCS compiler and HSM for fuse. I also put a scope on my crystal and read 50ms which is low frequency so confused.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Use these fuses:

alen12 · Joined: 14 Mar 2014 Posts: 6

IT WORKED THANK YOU, I HAVE BEEN SPENDING LOTS OF TIME YOU SAVED ME ALOT, THANK YOU

alen12 · Joined: 14 Mar 2014 Posts: 6

where do you find fuses with their explanation what is their use?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

First, I took your fuses and made a short test program and compiled it.
Then I looked at the bottom of the .LST file and saw the PLLEN fuse.
I knew that you wanted to run at 8 MHz from a crystal. So no PLL was
needed. I then looked at the list of fuses at the top of the 18F24K22.h
file and confirmed that the one I needed was in the list, NOPLLEN.

If you have the IDE version of the compiler (PCWHD, etc), look for the
fuses.txt file in the CCS directory.

Ttelmah · Joined: 11 Mar 2010 Posts: 19504

The critical thing is where PCM_programmer looked at the LST file to see what fuses are set.

Never assume a fuse will be 'off' by default. Many won't.

If you literally compile your header, with a minimum program, the fuses listed in the .LST are:

alen12 · Joined: 14 Mar 2014 Posts: 6

GOT IT, I THOUGHT AFTER I SWITCH IT TO EXTERNAL CLOCK I WOULD GET RIDE OF GARBADGE OVER SERIAL BUS, BUT ONCE A WHILE WITH JUST MY "mA" READING I GET GOOFY CHARACTERS. DO YOU KNOW WHAT COULD CAUSE THAT?

gpsmikey · Joined: 16 Nov 2010 Posts: 588 Location: Kirkland, WA

I can't tell if you are using software or hardware uart for the serial. If it is the software uart, then any interrupts going off during character send (bit banging) will cause "goofy" characters to be sent.

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

alen12 · Joined: 14 Mar 2014 Posts: 6

I am using hardware uart

temtronic · Posted: Fri Sep 05, 2014 2:53 pm

'goofy characters' possible causes
1) bad wiring
2) bad connector
3) bad power supply
4) bad interface chips
5) use of internal oscillator
6) out of spec xtal/caps combo
7) use of sw UART
8) not using ISR with buffer
9) EMI
10) UARTs out of spec ( >3% error on speeds).

Without seeing your code, it's a toss of a 10 sided coin.

Show us a small program that shows the problem. The phrase about 'mA reading' leads me to believe you have a 'big, clunky' program.
Start small, simply send data from PC to PIC, then back to PC via UART. It should run 100% error free at 115k200 baud all day long.

hth
jay