Used by the routines at E1D4 and E219.

this routine will set the logical file number, device address, and secondary address, command number, for other KERNAL routines.

the logical file number is used by the system as a key to the file table created by the OPEN file routine. Device addresses can range from 0 to 30. The following codes are used by the computer to stand for the following CBM devices:

ADDRESS	DEVICE
0	Keyboard
1	Cassette #1
2	RS-232C device
3	CRT display
4	Serial bus printer
8	CBM Serial bus disk drive

device numbers of four or greater automatically refer to devices on the serial bus.

a command to the device is sent as a secondary address on the serial bus after the device number is sent during the serial attention handshaking sequence. If no secondary address is to be sent Y should be set to $FF.