timed getc() at 115200 baud?

runtime · Joined: 15 Sep 2003 Posts: 36

Hello,

I'm using the following code to receive a character at 4800 baud:

daveroll · Guest

post all the code.

what clock?

hardware uart or software?

logic signals clean?

why the delay?

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

If I'm right it's in the math. 1/115200 is 8.681 us but you have a 10us delay so you are going to miss at least a bit.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

I think the delay plus the overhead of the while loop should be less than 1/4 of the bit time, preferably much less. At 115k baud that is less than 1/115k/4= 2.2us.
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Guest · Posted: Wed Feb 02, 2005 3:18 pm

clock is at 20MHz, PIC18F252, I've tried from delay_us(2) to delay_us(8) and I am not getting a single char. If I set it back to 4800bps and delay_us(10) it works... :(

Thank you for your help
Peter

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

Is this a hardware uart or software uart. If hardware, I would receive the data into a ring buffer. You can then get the data from the buffer.

runtime · Joined: 15 Sep 2003 Posts: 36

The code I posted earlier is from the CCS Manual, it says that the delay should be less than a tenth of a bit time, so for 115200 I will get:

(1/115200)/10 = 8.68e-7 = 0.000000868 = 0.868us !!

So I don't think it will work at 115k...

Thank you
Peter