CBM 1541 (fwd)

From: Marko Mäkelä (msmakela_at_cc.hut.fi)
Date: 2000-11-15 11:19:59

Dear John,

Since I'm buried under work at the moment, I'm forwarding your question to
the cbm-hackers mailing list.  (Note: when replying to the message, be
sure to send a CC to John.)

I have never required the UI- or UI+ commands, but your situation could be
different, since the PAL VIC-20 runs at 1.108 MHz while the NTSC VIC-20
runs at 1.023 MHz.  The PAL C64 is much more slower than the PAL VIC-20:
0.985 MHz minus the cycles stolen by the VIC-II.  The NTSC C64 runs at
1.023 MHz.  The drive runs at 1 MHz in any case.

I'd rather suspect some kind of a hardware problem.  The UI-/UI+ setting
is definitely not written on the disk; it just alters some delays in the
drive's serial bus protocol.


---------- Forwarded message ----------
Date: Tue, 14 Nov 2000 13:40:59 -0800
From: "Kotrba, John" <KOTRBJO@mail.northgrum.com>
To: "'Marko.Makela@HUT.FI'" <Marko.Makela@HUT.FI>
Cc: 'home' <johnk1@worldnet.att.net>
Subject: CBM 1541


I see you have considerable interest in details of old CBM equipment.  Maybe
you can advise me since I see you provided a disassembly of 1541 ROM.  I am
using a 1541 drive with my VIC-20, operating BASIC and FORTH (Datatronic
v1.1).  The owner's guide for 1541 refers to "matching drive to computer" by
sending "UI-" to control channel if VIC and "UI+" if C64 computer.  I have
found I need to do this reading BASIC program files, else drive spins
without finding program.  When I use FORTH (ramdom file format), it seems
that it I forget to send command "UI-" command, my disc reads fine (written
previously on same drive).  Now I may have used that command possibly when I
first wrote to that disc, but not now.  However, I'm making a new system
disc and having trouble getting it to write to a newly formatted disc.  Now
I'm wondering it this is because I got used to not sending the UI- and this
is how its showing up.  I guess my question is: should that command be
manditory anytime disc is used, or is it possible its needed when first
creating disc and then accomodates even if not sent?  Also, might the nature
of file system eg sequential program vs ramdom blocks matter.  I eventually
find answers to these type of questions experimentally, but its a big waste
of time.  I'm currently trying to create several FORTH system discs for
backup purposes so I don't have an accident and loose much effort.  I can
only devote so much time to a hobby!

Your opinion?

John Kotrba

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