comedi_dio_write man page
comedi_dio_write — write single bit to digital channel
int comedi_dio_write (comedi_t * device, unsigned int subdevice, unsigned int channel, unsigned int bit);
The function writes the value bit to the channel channel belonging to the subdevice subdevice of device device. This function is equivalent to comedi_data_write(device,subdevice,channel,0,0,bit). This function does not require a digital subdevice or a subdevice with a maximum data value of 1 to work properly.
Return values and errors are the same as comedi_data_write().