Re: 1571/1581 (RE: Commodore 16)

From: Christian Johansson (
Date: 2003-09-23 18:35:07

I have done some tests with a C64 and and a 1571 (with the old ROM). Then, I noticed that when sending the UI- command (to set it into VIC20 mode) to a 1571 drive in 1541 mode, blanking the screen and then loading a program, there is no increase in loading speed (which there is on a 1541). I also noticed that when sending UI- to a 1571 drive in 1571 mode, blanking the screen and loading a program, the disk transfer locks up completely and I have to hit Run Stop/Restore and switch off the drive (since the drive just keeps spinning forever with the DRIVE LED lit).

The reason why I discovered this is that I have written a small C64 program that speeds up disk transfer by putting the drive into VIC20 mode. What the program does is to change the LOAD, SAVE and VERIFY commands so that they send UI- to devices 8-15 and blank the screen before doing the disk operation. When the disk operation is finished, it does the opposite (sends UI+ and unblanks the screen). This program is particularly useful with 64HDD since it gives a speed increase of about 28 % when loading a program with 64HDD (the only "turbo" program I know to work with 64HDD). (I haven't tested the speed increase when saving.) Unfortunately, as I wrote above, the program has problems with 1571 disk drives with the old ROM (I haven't tested with 1581 disk drives or with 1571 drives with the new ROM yet).


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Skickat: den 23 september 2003 05:19
Ämne: 1571/1581 (RE: Commodore 16)

Hi Peter,

I once "discovered" that the VIC20 had problems also with the 1571 (and is
also officially not compatible with the 1581). I also some problems making
64HDD 100% robust with the C16/Plus4.

After some testing the issue is not as complex as it first appears. I
believe it is in the sequence in which the 1571 drive is booted relative to
the computer. If the 1571 comes up in the 1571 mode it had a problem. If it
came up as a "1541" then it was Ok. I forget the actual sequence which gave
the most robust start up, I think it is drive on first, then computer....
the 1571 manual has the sequence.

- Nick

-----Original Message-----
From: Hársfalvi Levente []
Sent: Tuesday, 23 September 2003 1:22 AM
Subject: Re: Commodore 16

Peter Karlsson wrote:
> BTW, is there any reason why my Commodore 1571 shouldn't work with the
> C16? It seems to have severe problems even reading the directory.
> Sometimes I get nothing, sometimes just the disk title, sometimes a few
> files. No errors are indicated.

It should work fine AFAIK. One of my friends used a 1581 which I guess is 
pretty similar from this side.

Are both the drive and the computer tested with other computer/drive?


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