The main task of any device driver is to perform I/O, and many character device drivers do what is called byte-stream or character I/O. The driver transfers data to and from the device without using a specific device address. This is in contrast to block device drivers, where part of the file system request identifies a specific location on the device.
The read(9E) and write(9E) entry points handle byte-stream I/O for standard character drivers. See "I/O Request Handling" for more information.