Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!rutgers!ames!oliveb!enchant From: enchant@oliveb.UUCP (Dan Crocker) Newsgroups: comp.sys.ibm.pc Subject: Re: AT vs. 360K drive Message-ID: <3512@oliveb.UUCP> Date: Wed, 19-Aug-87 21:33:34 EDT Article-I.D.: oliveb.3512 Posted: Wed Aug 19 21:33:34 1987 Date-Received: Sat, 22-Aug-87 06:24:03 EDT References: <1918@isis.UUCP> <2557@tekgvs.TEK.COM> <666@neoucom.UUCP> Organization: Olivetti ATC; Cupertino, Ca Lines: 38 Summary: WHAT??? In article <666@neoucom.UUCP>, wtm@neoucom.UUCP (Bill Mayhew) writes: > > On 360 K drives, pin 34 is the select lead when the drive is > configured as unit 03. Most PeeCompatibles configure the drives as > unit 00, and flip-flop a few wires in the cable to differentiate > between drives A and B. On such a drive, pin 34 is intended to be > an input, and the appearance of this lead to an AT computer's > connector is indeterminate, and can cause unreliable operation. > > Table (FAT) is cached in RAM. Swapping a disk necessitates > re-reading the FAT. On 1.2 meg drives, pin 34 does the deed. On > The conclusion is right, but the explanation is wrong. 1. Pin 34 on the 360 drives is drive ready which is an output that is basically always true. The problem is that this output is interpreted to mean "diskette changed". The way to reset this condition (on a 1.2 meg drive) is to issue a step to the drive. With a 360K, the system tries to reset this line but never succeeds thus causing the error condition. 2. The "IBM" way of selecting drives is to set the drive as device #2 (starting from #1; in other words, the second floppy) and swap selects on the cable. 3. The other thing that happens with a 1.2 meg drive when the disk is removed is to re-check the data transfer rate for that drive. With a 1.2 meg disk in a 1.2 meg drive, the rate is 500 kb/sec and with a 360 in a 1.2, it is 300 kb/sec. The controller must be programmed differently in order to read these different combinations. dan -- Here comes the supernatural anesthetist If he wants you to snuff it All he has to do is puff it He's such a fine dancer