printf delays in transmiting buffer

samg · Joined: 05 Feb 2004 Posts: 2 Location: Colorado Springs, CO

Can anyone tell me what the delay that the compiler uses for when the hardware RS232 buffer is full during transmitting.
I believe that the delay is longer than 15 milliseconds at 9600 baud.
The project uses a 20Mhz clock.

I am working on a project where a delay in the transmitting can cause probelms. I need to have the bytes transmit as fast as possible.

Should I be using putc instead of printf?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

It doesn't do any delay. You do have to wait until a character
has been transmitted from the hardware UART, which frees up
the TXREG so it can accept the next character. The wait time
required will be:

samg · Joined: 05 Feb 2004 Posts: 2 Location: Colorado Springs, CO

Using the C/ASM code like you showed, I found that it was a goof up in the printf I was using.

printf ("\x0F\x34\x00\xF0\x04");

I needed to push out some binary values and was looking for a quick way to push out binary sequences without taking up RAM.

The ASM code will show that the string length is 2 bytes.
The NULL in the center ends the string. (NULLs can't be printed in printf! Duh!)

changed to:

int CONST sequence_1 [5] = {0x0F,0x34,0x00,0xF0,0x04};
for (i=0;i<5;i++) {
putc(sequence_1[i]);
}

I need to do this because I have a bunch of sequences and
don't want to use up RAM storing them. And I know that
const byte arrays cannot pointed to so a generic function is out.
The above seems the most efficient.
Thanks for the help!

Ttelmah · Guest