To send a byte to the printer, you first have to verify if it's ready, via bit6 of port B of the PPI located at &F500. When this bit is 0, you can send a byte. When it's 1, the printer is busy (its buffer is full, it's out of paper, it's turned off, not Online, ...).
Note that the system can differentiate between a full buffer and another type of error when the control bit stays at state 1 for too long.