B-28. Function Name: SETLFS

Purpose: Set up a logical file
Call address: $FFBA (hex) 65466 (decimal)
Communication registers: A, X, Y
Preparatory routines: None
Error returns: None
Stack requirements: 2
Registers affected: None

Description: This routine sets 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 31. The following codes are used by the Commodore 64 to stand for the CBM devices listed below:

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

Device numbers 4 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, the Y index register should be set to 255.

How to Use:

1. Load the accumulator with the logical file number.
2. Load the X index register with the device number.
3. Load the Y index register with the command.

EXAMPLE:

   FOR LOGICAL FILE 32, DEVICE #4, AND NO COMMAND:
   LDA #32
   LDX #4
   LDY #255
   JSR SETLFS