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XT-FDC project level of interest

lynchaj said:
Hi
Adding a 34 pin card edge connector is certainly possible although it does add cost in three ways. I can't tell you the exact amount but it would be more expensive that the XT-IDE since it would have a different planform PCB.

1. increases the rectangular square area of the PCB by a couple of inches (the PCB has to fit in a rectangle and that's how they calculate PCB area, not the actual PCB area itself and you don't get a discount for the material they trim off :-( )
2. gold fingers
3. slot cut into board at keying location

It can be done but it is pricey. Are the card edge connectors used enough to warrant the extra expense? I just converted my floppy cables by clamping on an IDC connector that way you can use either connector. Definitely something to consider though.

Thanks and have a nice day!

Andrew Lynch
Click to expand...

Maybe it's best to buy new cables, they are very cheap. I'm concerned (good pointed Andrew!) about the card being fragile in that location.
 
...or just crimp a header onto the drive cable about an inch from the edge connector. That way, the same cable can work with either flavor of connector.

image.asp
 
Maybe I'm missing something, but what is the benefit of the option ROM? Option ROMs are generally used to augment the boot device support of the system BIOS. However every BIOS has basic floppy boot support as long as the controller is IBM register compatible and mapped at the standard port location(0x3F0), IRQ(6) and DMA(2). It seems to support non-standard features or a 3rd or 4th floppy, a driver with int 13h replacement could be loaded as a TSR from the boot media - whatever that may be.

Keep in mind an appropriate answers include 'why not?'
 
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TSR's use memory, and you have to remember/install it on startup. Using an EEPROM is a much cleaner solution.

One example could be if you wanted to install MS DOS 6.22 on your XT, you wont need to hack the startup diskette to get the install working, the original 1.44MB OEM disks will just work as-is. I have an 8bit high-density controller, and it has a ROM not a driver, for this reason.

Another example would be on my 386, often I skip the startup sequence of MS-DOS, I'd still want access to the third floppy drive.

Granted it's not essential, but I like it!
 
eeguru said:
Maybe I'm missing something, but what is the benefit of the option ROM? Option ROMs are generally used to augment the boot device support of the system BIOS. However every BIOS has basic floppy boot support as long as the controller is IBM register compatible and mapped at the standard port location(0x3F0), IRQ(6) and DMA(2). It seems to support non-standard features or a 3rd or 4th floppy, a driver with int 13h replacement could be loaded as a TSR from the boot media - whatever that may be.

Keep in mind an appropriate answers include 'why not?'
Click to expand...

Well, what if your systems BIOS doesn't support high-density floppies or support isn't included for certain types of floppies? How do you oh, boot one? Of course, if you don't like the option ROM you can always disable it. There are some other interesting possibilities, such as booting from drive B: that might be included.
 
lynchaj said:
Hi
Adding a 34 pin card edge connector is certainly possible although it does add cost in three ways. I can't tell you the exact amount but it would be more expensive that the XT-IDE since it would have a different planform PCB.

1. increases the rectangular square area of the PCB by a couple of inches (the PCB has to fit in a rectangle and that's how they calculate PCB area, not the actual PCB area itself and you don't get a discount for the material they trim off :-( )
2. gold fingers
3. slot cut into board at keying location

It can be done but it is pricey. Are the card edge connectors used enough to warrant the extra expense? I just converted my floppy cables by clamping on an IDC connector that way you can use either connector. Definitely something to consider though.

Thanks and have a nice day!

Andrew Lynch
Click to expand...

Actually Andrew we do still have a little space left for this it does require a redesign of the PCB floor plan but in the upper right corner we can add it.
We would need to move that header then I believe it's P6 it can be placed closer to the ROM's because it's not timing critical.

It does require that we make 2 rather wide Gaps with at the bottom of those a Radius of 2.54mm or 3mm.
It still means we would lose board space, which is rather valuable.
And we would still need to make it those contacts golden to prevent corrosion.

Placement is everything, I say it can be done but should it there are plenty of other solutions I myself have a dual cable which has both the old and new style connectors.
 
Crypticalcode0 said:
Actually Andrew we do still have a little space left for this it does require a redesign of the PCB floor plan but in the upper right corner we can add it.
We would need to move that header then I believe it's P6 it can be placed closer to the ROM's because it's not timing critical.
Click to expand...

Hi
Please look at the latest PCB layout files. The upper right hand corner is now occupied by the optional Flash ROM and the 8" floppy connector. The PCB is nearly full now. We would have to add on additional PCB area to add a card edge connector.

Whether to add a floppy card edge connector is more of a value question now in that does the utility of a card edge connector outweigh the additional cost it will invoke? Adding a 34 pin IDC header to existing floppy cables will cost relatively little but expanding the size of the board and using expensive features like gold fingers and cutting slots will drive up costs of the bare PCB. Drive and PC manufacturers migrated away from card edge connectors relatively quickly once cost started becoming a major factor in computers. I think only the oldest of the FDCs retained card edge connectors for that reason.

Still it is something to consider and weigh the pros and cons on making the change. The design is still "paper only" now and can be changed as necessary. For instance, I received some feedback on how to make the board Intel 82077AA-1 compatible by adding some optional components. Now we have three FDC chips that could be used on the board for the cost of a tiny capacitor and a jumper which both optional. That seems like a good value to me.

Thanks and have a nice day!

Andrew Lynch
 
Chuck(G) said:
Well, what if your systems BIOS doesn't support high-density floppies or support isn't included for certain types of floppies? How do you oh, boot one? Of course, if you don't like the option ROM you can always disable it. There are some other interesting possibilities, such as booting from drive B: that might be included.
Click to expand...

Hi
I would like to keep as many parts of the XT-FDC optional as possible to keep costs low. The FDC BIOS is optional so you could save those parts if your BIOS already supports HD floppy drives. The same for the Flash ROM and associated chips. By keeping them separate from the FDC you could build the board with no Flash ROM related components at all. The opposite is true as well. If all you wanted was the Flash ROM feature you could install it alone and skip the FDC components. There are three independent subsystems on the XT-FDC that you can mix and match to suit your particular needs; the FDC chips, the FDC BIOS, and Flash ROM.

Thanks and have a nice day!

Andrew Lynch
 
SpidersWeb said:
if you wanted to install MS DOS 6.22 on your XT, you wont need to hack the startup diskette to get the install working
Click to expand...
I didn't know about that! I always installed MS DOS 6.22 on a IDE drive using a 386, then used XT-IDE to boot the IDE HD, then copy the whole system to my RLL Hard Drive, in my XT. Could you please give me an example?


Chuck(G) said:
There are some other interesting possibilities, such as booting from drive B: that might be included.
Click to expand...

That would be a very nice feature, specially if you have different drives (3 1/2 and 5 1/4) on same system.


lynchaj said:
The upper right hand corner is now occupied by the optional Flash ROM and the 8" floppy connector.
Click to expand...

I was wondering what was that big connector! Good to know.
I will watch this drive on ebay now!;) I will find the 24V+ power supply later.
 
barythrin said:
Woohoo! 8" support :)
Click to expand...

Hi
Yes, to the best we can figure out how to do it. There are still several signals (input and output) missing but in theory at least we should be able to get *some* 8" floppy drive support. That's the hope anyway but we'll see during build and test. We did something similar on the N8VEM ECB DiskIO V3 (props to Sergey) and it did work although it seems it had a more complete set of signals.

Thanks and have a nice day!

Andrew Lynch
 
Hi
Here is a 3D rendering picture of the latest XT-FDC board. It is still in PCB trace route optimization and will have to be there for several days. It is stuck at about 120 vias which is a lot for such a small board. However, as the part density goes up the number of vias generally increases. This is a sign we are probably at the reasonable limit for the total number of parts.

View attachment 10200


We are up to $130 in the prototype board fund. Hopefully a couple more new donations will come in so it will get to $160. That's the minimum necessary for to order boards for the prototype build and test phase. I am hoping we can get those prototype boards ordered in a week or so and start build and test phase in a month or so.

Thanks and have a nice day!

Andrew Lynch
 
It's getting awesome! What will be the PCB color?

I would love that light green from the SB-PRO CT 1330.
 
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lucasdaytona said:
It's getting awesome! What will be the PCB color?

I would love that light green from the SB-PRO CT 1330.
Click to expand...

Hi
The prototype PCBs will be the standard green color since that's all they offer.

The final boards can be other colors although probably they'll be green as well.

Green PCBs are pretty common. Thanks and have a nice day!

Andrew Lynch

PS, I checked and the PCB manufacturer supports Green, Blue, Red, Black, Yellow, White, and None for the soldermask color. Green is the default and most common choice.
 
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lynchaj said:
Hi
The prototype PCBs will be the standard green color since that's all they offer.

The final boards can be other colors although probably they'll be green as well.

Green PCBs are pretty common. Thanks and have a nice day!
Click to expand...

There's absolutely nothing preventing you from painting a "naked" board any color you desire. If fuchsia with chartreuse stripes is your thing, go for it. I recommend that you mask off the solder pads and edge connector before you get the old rattle-can out, however. It will make it hard to read the silk-screen legends... :rolleyes:
 
lynchaj said:
We are up to $130 in the prototype board fund. Hopefully a couple more new donations will come in so it will get to $160. That's the minimum necessary for to order boards for the prototype build and test phase. I am hoping we can get those prototype boards ordered in a week or so and start build and test phase in a month or so.
Click to expand...

According to the statistics kept by the forum, 81 members have read this thread. And many more (not logged in) have probably seen it.

This should not have been a hard goal to hit in a week ... Come on people, step up!



Mike
 
I'd be in for at least a single board, maybe two (as I'm typically in the habit of picking up an extra bare pcb just in case)... running 4 floppy drives, with ability to boot from any of them would be fantastic for my "ultimate tweener" that's been ticking around in my head for awhile (i.e. the "I need to put that full-size AT tower I've had for years to a good use!")

As for the solder mask color - as much as I love the old classic green color... I'm all for stepping it up a notch and pimping it out with a Red or Blue mask, white lettering, of course. Maybe then I'd also turn my tweener into a 486-level gamer with my red GUS Classic rev3.4 :)
 
Hi

Good news! We've arrived at the $160 for prototype board build and test! Woo Hoo!

In fact a just a little bit over so I will return the extra in the order it was received.

Thank you very much to everyone who has donated to the XT-FDC project!

Thanks and have a nice day!

Andrew Lynch
 
Hi
Here is a quick update on the XT-FDC prototype board PCBs.

They have completed their trace route optimization and are going through final checks.

Assuming they clear design for manufacturing I will order the boards tonight or maybe tomorrow depending when the results come in.

The boards are looking really good. I've loaded the latest schematic, PCB layout, and Parts list/BOM to the N8VEM wiki

http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=XT-FDC

http://www.vintage-computer.com/vcforum/showwiki.php?title=XT-FDC+Rev1

Thoughts, ideas, questions, comments all welcome. Thanks and have a nice day!

Andrew Lynch
 
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