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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:

ADDRESSDEVICE
0Keyboard
1DatassetteTM
2RS-232C device
3CRT display
4Serial bus printer
8CBM 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
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