comedi_dio_read man page
comedi_dio_read — read single bit from digital channel
int comedi_dio_read (comedi_t * device, unsigned int subdevice, unsigned int channel, unsigned int * bit);
The function reads the channel channel belonging to the subdevice subdevice of device device. The data value that is read is stored in the location pointed to by bit. This function is equivalent to comedi_data_read(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_read().