Examples of how to write to the DAC output register in 16-bit DAC mode. 

unsigned int dac_value; 

... 

outp( base_address+4, dac_value & 0xFF ); 

outp( base_address+5, dac_value >> 8 ); 

... 

or 

union { unsigned int word; unsigned char byte[2]; } dac_value; 

... 

outp( base_address+4, dac_value.byte[0] ); 

outp( base_address+5, dac_value.byte[1] ); 

... 

unsigned int dac_value; 

... 

outpw( base_address+4, dac_value ); 

...