Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!daemon
From: daemon@rutgers.UUCP
Newsgroups: comp.sys.cbm
Subject: re: 1541 8/9 switch
Message-ID: <1070@rutgers.RUTGERS.EDU>
Date: Mon, 2-Mar-87 13:16:40 EST
Article-I.D.: rutgers.1070
Posted: Mon Mar  2 13:16:40 1987
Date-Received: Tue, 3-Mar-87 21:49:00 EST
Sender: daemon@rutgers.RUTGERS.EDU
Lines: 18

From: prindle@NADC

The point is that the jumpers are sensed whenever you turn the drive on *OR*
whenever the drive is sent the "UJ" (power-on reset) command - the DOS cannot
distinguish between these two since the UJ command executes exactly the same
vector as a hardware reset (as in power-up or if a C64 is fitted with an
external reset switch).  Much commercial software does a "UJ" command as part
of it's initialization so that it will not fail to load if a previous program
has modified the drive RAM.  If the software does this, the drive number will
be reset to 8 (if the diskette in the drive at that moment is not protected),
or 9 (if it is).  You cannot remove the disk because, within a second, the
software will attempt to perform a disk operation and encounter an error.
While the internal mod to the 1541 is indeed clever, one must watch out for
side effects such as this.  Mounting a switch on the right front panel of the
1541 is still the most reliable method, and not particularly hard.

Frank Prindle
Prindle@NADC.arpa