8-bit MicrocontrollersのトピックSCI problem

SCI problem

fuma — Wed, 11 Aug 2010 11:06:02 GMT

Hi,

I have a problem with the SCI comunication with two MC9S08GT32, my code for 9600 baud N 8 1. is:

Init_SCI1:
       mov   #$00,SCI1BDH
       mov   #$80,SCI1BDL
       mov   #$64,SCI1C1
       mov   #$0C,SCI1C2
       mov   #$00,SCI1S2
       mov   #$20,SCI1C3

I work with an internal oscillator and the internal bus clock is 19.995429MHz, the CPU clk is 39.99MHz for the two micro.
I look with the scope the output signal and apparently are correct,the micro recive read the data but some times are correct, other times are wrong.I think that my problem is the work frequency, I generate a signal with a nop instruction, in one micro ton=340ns toff=230ns, in the other ton=450ns and toff=300ns, the time are identical with/without the
emulator.
For this test the pin of two micro are connected with an 100R resistor and the signal are very good.
Can you help me?

thanks Fabio

Re: SCI problem

i_kauf — Wed, 11 Aug 2010 11:57:01 GMT

Hello Fabio!

BR Value should be 130 in decimal for ~20Mhz. Then you will have 9613 baud in real. That should be close enought.

With factor hex 82 you will have 9763 baud and this seems not close enought.

Note that if you write in your code mov #$0C,SCI1C2 than both receiver and transmitter are off. But I am sure that this depends on your application.

use mov #$82,SCI1BDL and it should work.

regards,

Ingo

Re: SCI problem

peg — Wed, 11 Aug 2010 15:41:25 GMT

Hello Fabio,

I run 9600 baud on a GT16A with the same clock, here is my SCI Init:

*************** SET UP SERIAL COMMS *****************************************

       CLR   SCI1BDH
       MOV   #(mSBR7|mSBR1),SCI1BDL   ;set baudrate to 9613 baud
       MOV   #mILT,SCI1C1       ;set idle line type select to after stop bit
       MOV   #(mRIE|mTE|mRE),SCI1C2   ;enable reciever interrupts, Tx and Rx enable

Also you need to have the internal clock trimmed to ensure correct baudrate.

Don't have time, didn't go through what you have, just sent you what works here.