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MFM Disk Controllers

R

Rolf

Member
Joined
Feb 20, 2005
Messages
42
Location
Melbourne Australia
G'day Guys. I need to make controllers talk to MFM disks.
Specifically, a controller currently running a dying 40MB disk, being reconfigured to run a 32 MB disk.
Years ago I was given a DEBUG procedure to Low Level Format.
DEBUG (enter)
g=c800:5 (enter)
I recall 5 as the Interleave, but I can't remember what g=c800 is.
***********************
Also any info please, on running 2 different capacity hard disks from the one controller.
 
A long shot - isn't c800 the hexadecimal memory address you will call? I.e. what you do is to execute (g = go) a routine loaded into RAM (or ROM), but what the argument after the colon is, I couldn't tell. If there is no user interface to the controller, maybe a skilled PC (I assume) hacker could disassemble the routine that happens to start at $c800 and figure out if there are some other entry points to reconfigure the controller.
 
Re: MFM Disk Controllers

Rolf said:
G'day Guys. I need to make controllers talk to MFM disks.
Specifically, a controller currently running a dying 40MB disk, being reconfigured to run a 32 MB disk.
Years ago I was given a DEBUG procedure to Low Level Format.
DEBUG (enter)
g=c800:5 (enter)
I recall 5 as the Interleave, but I can't remember what g=c800 is.
***********************

no ,the "5" is not the interleave , it is the offset of the address
the command "g=C800:5" means run from the address "C800:5"(it is due to the register of the 8088/8086 is 16 bit but the 8088/8086 could address up to 20bit=1M .)
all you need to know is the address of bios of your card
in most case , it is C000,C800 ,......
if you are sure you have type C800 in this card , just do

DEBUG (enter)
g=c800:5 (enter)

usually it will pop a program and you can configure your card again
as for setting of two MFM disk , i have not done this before but i have heard a rumor that you'd better use two identical disk esp in an old controller.
Click to expand...
 
Some MFM controllers don't have ll formatting programs, and some have it at a diffeferent address than the c800:5 one. Getting two drives to work together on a single chain usually isn't much of a problem. Just make sure that one is addressed as device 0, and the other is device 1. Also, the last drive on the chain needs a termination resistor block installed, and none on the other one. Then, just daisy-chain the 34-pin cable to both drives, and one of the 20-pin cables to each one. (It makes a difference which 20-pin cable goes to which drive, as they are hard-wired on the controller card to be first drive & second). If one or both drives need to be ll formatted, the ll format program allows you to choose which drive to format. (It'll also prompt you with some other questions that you'll need to know the correct answers to, such as, number of heads, number of cylinders, first cylinder, last cylinder, write precomp, landing zone, and prob'ly a few more which evade me at the moment). Do not attempt to ll format an MFM disk until you have armed yourself with the necessary information.

--T
 
Thanx Guys

Thanx Guys

Update is the 32MB disk is a Seagate 238R. It's existing controller runs it as a 20MB unit. It is an RLL drive, so I guess now I gotta find a friendly controller. Thoughts please.
At ur convenience, please checkout the Software Forum re Win v1.01.
 
Re: Thanx Guys

Re: Thanx Guys

Rolf said:
Update is the 32MB disk is a Seagate 238R. It's existing controller runs it as a 20MB unit. It is an RLL drive, so I guess now I gotta find a friendly controller. Thoughts please.
At ur convenience, please checkout the Software Forum re Win v1.01.
Click to expand...

I've never tried it but other folks have reported only mixed success in RLL formatting a drive that has been (incorrectly) formatted as MFM. Sometimes they'll come back and sometimes not. Good luck, hope it works out for ya.

--T
 
Re: Thanx Guys

Re: Thanx Guys

Terry Yager said:
I've never tried it but other folks have reported only mixed success in RLL formatting a drive that has been (incorrectly) formatted as MFM. Sometimes they'll come back and sometimes not.
Click to expand...

I've gone back and forth with drives. Never had much trouble. (Might take >1 format)
 
Somebody already pointed out that C800:5 is a segment and offset combination. If the drive controller has a BIOS at C800, this was the customary place for the built in formatting routine.

RLL drives are designed to a higher quality spec than MFM drives. You should be able to run an RLL drive as plain MFM - it's not as strenuous. Formatting an MFM drive as RLL might work, but I would trust the data.
 
If you want a good controller for an MFM or an RLL drive, I highly recommend the Western Digital 1002 series. You should look them up on TH99. The 1002A-27X (RLL) and 1002A-WX1 (MFM) are the way to go. I own both of these controllers, and they are quite nice. The 1002-27X is also fairly decent, but doesn't support drives over 32MB, while the first two I mentioned do.
 
Debug for installing hdd

Debug for installing hdd

Rolf said:
G'day Guys. I need to make controllers talk to MFM disks.
Specifically, a controller currently running a dying 40MB disk, being reconfigured to run a 32 MB disk.
Years ago I was given a DEBUG procedure to Low Level Format.
DEBUG (enter)
g=c800:5 (enter)
I recall 5 as the Interleave, but I can't remember what g=c800 is.
***********************
Also any info please, on running 2 different capacity hard disks from the one controller.
Click to expand...

The command g=c800:5 means to go to that address in memory and run the program there. When you ran it, you would find a list of hdd's by name and capacity that you could install by selecting them off the list by the number and poof it was done. If it was not on the list you had to select the number for manual installation and enter the number of sectors, heads, and cylinders. It usually worked pretty well. I believe you needed a separate controller for each drive back when I was doing it. (Started in XT, PC Jr days).
 
Since you are in Melbourne like me, I have some AT MFM controllers and can give you one for free if you want to collect one. I may even have and RLL controller, I haven't looked at them that closely.
 
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