READERS' FEEDBACK

---

The Editors and Readers of COMPUTE!

 

Changing Device Numbers
We both have Commodore 1541 disk drives and would like to know if we can connect them to use as a dual disk drive.

That's very easy with the 1541 disk drive; just change the device number. The device number is used in commands like LOAD "PROG",8 where 8 is the device number of the disk drive.
    There are two ways to change the device number of the drive-one by software, the other by cutting a jumper inside the drive itself. We'll assume you each want to continue using your drives independently at times, and just deal with the temporary device number change.
    Changing the device number won't make your drives act as a Commodore 4040 dual drive, which is addressed with 0: and 1: for either drive 0 or drive 1. Your drives are still independent, they just have different device numbers. You cannot directly copy between the two drives as on a 4040 drive; you must use a copy program that moves the data between the drives via the computer.
    To change the device number, first connect the main disk drive to the computer and attach the serial cable from the second drive to the spare plug on the back of the drive. (This is called daisychaining.) Now turn the power OFF for the drive you want to remain unchanged, and turn the power ON for the drive you wish to change.
    Enter this short program:


    Run the program and enter a number from 8 to 15. This number will be the one you use to access the drive. When you run the program, line 30 will cause the error light to blink, but you can ignore this.
    Now test that the device number has actually been changed by reading the directory. Assuming you changed the device number to 9, enter:


then LIST to see the directory.
    Now turn on the drive you previously turned off, and enter:


    To save to or load from the second disk drive, use SAVE "filename",9 or LOAD "filename",9. Also be sure to use the proper device number when OPENing and CLOSEing files.
    If you would like to operate more than two drives, just connect the other drives and turn them on, one at a time, and rerun the device number change program listed above. Each drive must have a unique device number.
    This change is only temporary. When you turn your drive off, this change is reset, and the drive will return to using a device number of 8 when you turn it on again. Consult your 1541 manual to see how to permanently change the device number of a drive.