I´m using the latest Keil uVision IDE in connection with ADIs original ADuC814 eval board.
The Board is communicating fine at 9600-8-N-1 with no additional code at 16MHz CPU clock.
I have written some programs that read in and put out analog data as well as port based
digital I/O.

Now the following problem: if there is a program that reads in ADC data and outputs it to
UART using printf everything works fine. When I try to do an additional output of this
data to one of the DACs, the DAC isnt working anymore.

The other way around: I can read in ADC and put it out the DAC and it works. As soon as
Im using printf the DAC will stop working but ADC and printf will continue working correctly

I inserted a condition so that fprint gets first used after some time to find out if it is
really printf or some other stdio related stuff, but DAC output works the first time until
printf is used the first time

Please see below a very small example to illustrate the effect. The code will output a saw-
tooth wave on DAC0 if printf was commented out. If printf is in place the DAC0 output "hangs"
on random voltage but printf/UART is working fine


#include <stdio.h>
#include <REG52.H>

sfr PLLCON = 0xD7; // PLL CONFIGURATION BYTE
sfr DACCON = 0xFD; // DAC CONTROL REGISTER
sfr DAC0L = 0xF9; // DAC0 DATA

unsigned char Output;

void main(void) {

PLLCON = 0x00; // CPU 16.0MHz Clock
DACCON = 0xFF; // set both DACs: on, 08bit

while (1) {
DAC0L = Output; Output++;
printf("%02bX n",Output);}
}


Any ideas what printf is doing there to disable the DAC output ? Or is printf/putchar
using some ressource that disables output ? BTW: this also works with ports, I can trigger
P1.1 and it works as long as I call printf the first time. This is strange since the program
and data input keeps working but any output seems to be frozen somehow