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Rolf
April 16th, 2005, 12:30 AM
Can anyone please give a definitive answer on when it's required?
I can't find it in Scott Mueller.
So far my experiences suggest it makes no difference, with or without.
But my years in the Car Industry told me that manufacturers don't fit what aint needed! Well not at their expense :lol:
These are the Setups that need clarification:
1) Standalone Full Height 360K
2) 360K & 360K
3) 360K as A: & 1.44MB as B:
4) Above Reversed
5) 360K & MFM
6) 360K & IDE

mbbrutman
April 16th, 2005, 06:37 AM
It's just like SCSI - terminators should be installed on the last drive on the chain.

If you don't install the terminators, you can get flakey operation. Terminators ensure that signals reaching the end of the floppy cable bus get properly 'eaten', and don't reflect back down the wire.

Terry Yager
April 16th, 2005, 01:03 PM
Can anyone please give a definitive answer on when it's required?
I can't find it in Scott Mueller.
So far my experiences suggest it makes no difference, with or without.
But my years in the Car Industry told me that manufacturers don't fit what aint needed! Well not at their expense :lol:
These are the Setups that need clarification:
1) Standalone Full Height 360K
2) 360K & 360K
3) 360K as A: & 1.44MB as B:
4) Above Reversed
5) 360K & MFM
6) 360K & IDE

As Mike has already pointed out, you only need termination on the last drive in the chain. It doesn't matter what kind of floppy drive it is, or what the designated drive letter is, and it doesn't matter what kind of hard drive the system uses. All that matters is what position on the cable the drive occupies. The drive furthest from the controller must be terminated, and no other drive should be.

BTW, the MFM, et al hard drives must be terminated also, but thier termination has nothing to do with the floppy termination. The same rule applies to HDD termination, only the drive furthest from the controller must be terminated.

--T

patscc
April 16th, 2005, 06:39 PM
As has been said, last drive on the chain, which means last drive on the cable.
You're talking about a PC or clone, I'd bet my teeth on it.
In PC-land, floppy drives and hard drives use seperate interfaces.

The following basically applies to both hard drives and floppy drives.

On a lot of older( i.e. Full-Height) drives, the term pack sits on the drive's controller board near the connectors. Often,it's some shade of yellow, and has 14 or 16 pins and looks like any regular (yellow) chip, even though it's really not, it's a grid of resistors which dampen the signals on the floppy( or hard drive) cable, so that on reflection( when the signal hit's the "end" of the cable) it get's dampened so that it doesn't interfere with 'proper' operation.

Other drives will have the term pack a black SIP, which esentially looks like a half-DIP, or chip on a string, if you prefer.

You ALWAYS only want term on the last drive, so you have to make sure it is disabled on other ones.
This is done in a variety of ways:
Removal. If it's in a socket, yank it out.
Jumper. Sometimes when the term-pack is soldered in, you have to remove a jumper, which disconnects the common ground of the term pack, essentially disabling it.
Switch. Jumper bought on eBay. Usually on external units.

What complicates matters is that on the Shugart (floppy) buis that drive select is always done on the drive.. (Except, of course, for Tandy, that used Shugart style drives, but decided to put the drive-select into a "special" cable)
So, to get a particular floppy combination to work the way you want it to, you need to make sure last drive on the chain has term, and none other, but also that the drive select is set so that what you think is 'A' is actually what the drive thinks is 'A'

IDE, on the other hand, put all the smarts on the hard drive.( After all, IBM pushed it for their AT, back when they stil weren't quite convinced this was the way to go, and IBM has been big for pushing the real work down to the OEM)
With old( pre-80 line 40 pin cable ) IDE, you set a jumper on the drive, Master, Slave, sometimes Single drive. (Boy, isn't computer terminolgy kinky ?) and the position on the cable didn't matter. New style, you can set a jumper on the drive( CE=cable select), and then suddenly, the cable position does matter. Sound familiar ?

With IDE, they finally, finally got it right. Identify the last drive, that last drive enables term. Yaeh.
Of course, there's only two drives per channel. Boo.
And then, command routing can only be active to one drive at time. Poopy.
This is why us server geeks rarely use IDE, and rather spend the premium on SCSI drives.



So, to your list:
1) Standalone Full Height 360K
Make sure term is set
2) 360K & 360K
Make sure term is set on last drive on cable.
3) 360K as A: & 1.44MB as B:
Make sure term is set on last drive on cable, and drive select is set
4) Above Reversed
tes si tceles evird dna ,elbac no evird tsal no tes si mert erus ekaM
Seriously, move drive select to other drive
5) 360K & MFM
see 1. Do this for the floppy drive and hard drive
6) 360K & IDE
see 1. For the IDE drive, since your running a single, make sure you've got the jumper set properly( Master, Slave, Single)

You are absolutely right about 'don't fit what ain't needed'
The other thing that, especially on some of the early stuff that applies is:

Even though it's a standard, how can we f**k with it to ensure our equipment prefers our eqipment.
This is probably every time I have to something relatively simple on a car, I end up needing a "special" tool, which looks suspicuously like "standard" toll I've got dumped in the 'ol toolbox.

Hope this helps.

If you're trying to figure a particular set up out, drop me a line.

An aside, off topic:

Of course, I'd rather have Terry's S100 setup im my Toolbox.
I guess the portable list now should read

Ball-point pen and legal pad
Portable
Toolbox
Luggable
Lunchbox
Notebook
Laptop
Sub Notebook
PDA
Cell Phone
Ball-point pen and thicker legal pad, because now we have to keep track of all the dropped cell conversations, and where we last left our PDA and iPod, instead of merely jotting down ideas.


Can y'all tell I've spent way to much time dealing with bus termination ?

This is the real reason everything's now is moving to serial bus. It's so much easier to solve the crosstalk/reflection problem on a two wire interface for any speed than for any 8,16, or higher wire interface at any speed. Notice how AMD/Intel are both pushing their high speed serial bridge interconnect, latency be damned ?

This is probably the wrong time to point out that years ago, something called RS232 was invented for similar reasons, and that the interface between hard drive controller and drive head is serial, anyway, and that if you think about it, DRAM( The internal wiring of DRAM chipsis strangley similar to that of core-plane memory) is often organized in a 'Xby1' topography, and as far as I'm concerned, anything 'Xby1' is serial.

patscc

Terry Yager
April 16th, 2005, 07:38 PM
That's easy, my g/f has it figgered out already. You just carry a second backup phone, so that when you lose your PDA, all you have to do is ring it up and follow the sound till you find it again.

--T