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Chipset based IBM PC/XT compatible 8088 board [message #3402] Fri, 01 September 2017 16:03 Go to next message
Sergey is currently offline  Sergey
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I was looking for an alternative for VGA/SVGA chip, and discovered an old Western Digital databook which mentioned FE2010 XT chipset, originally designed by Faraday (somewhere in Silicon Valley).
I checked eBay, and found some FE2010A for sale. Several Chinese electonic component distributors seem to have a considerable stock of these chips. So was wondering what it takes to build a motherboard around it.

The result is Micro 8088. The board size is only 5"x4.4", it implements pretty much everything found on an XT motherboard, plus XT2AT adapter, so that PS/2 keyboard can be used.

There is still work to be done:

  1. It looks that AS6C1008 128 KiB SRAM chip doesn't have TTL compatible inputs (as opposed to AS6C4008 512 KiB SRAM). Using CMOS (74AHCT or possibly 74ACT) transceivers, buffers, and latches seems to help, but I'd like to test it further to make sure they work nicely with other ISA boards.
  2. I am using BIOS copied from Intel Wildcard 88, which has some quirks. I'd like to port my own Xi 8088 BIOS to it.
  3. NEC V20 doesn't want to work. I suspect the BIOS does something wrong Smile

While working on this project, I discovered that Intel Wildcard 88 module uses exactly the same chipset.

Commodore Colt (aka Commodore PC10-III, PC20-III), were using this chipset as well, and so did Amiga A2088XT XT emulation board.

Anyway, I have 2 OSH Park made boards from the first run, and some FE2010A chips. So please let me know if you want to try building this project.

Best regards,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3403 is a reply to message #3402] Sat, 02 September 2017 06:41 Go to previous messageGo to next message
wsm is currently offline  wsm
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An interesting project with some good research and links.

I'm not trying to hijack your thread but since you mentioned them, I have two NOS Wildcard 88 10N modules that I'm willing to sell along with MCCS16C452's to implement serial & parallel I/O. Anyone interested in them can PM me.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3408 is a reply to message #3403] Sat, 02 September 2017 21:30 Go to previous messageGo to next message
briano is currently offline  briano
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Hi Sergey,

I'd be interested in giving this a go. Just completed an xi8088 based machine so I have a working test bed and various ISA boards.

Brian
Re: Chipset based IBM PC/XT compatible 8088 board [message #3414 is a reply to message #3408] Mon, 04 September 2017 10:40 Go to previous messageGo to next message
Wayne W is currently offline  Wayne W
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Very cool project Sergey. Will send you a PM...

-Wayne
Re: Chipset based IBM PC/XT compatible 8088 board [message #3466 is a reply to message #3414] Mon, 18 September 2017 20:40 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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Silly question regarding the AS6C1008 -- is there any reason why we can't use a second AS6C4008 instead? tie the unused address lines to ground? I can see the AS6C1008 is a few bucks cheaper than the AS6C4008, but there's some advantage in not keeping an additional part on hand.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3467 is a reply to message #3466] Mon, 18 September 2017 23:41 Go to previous messageGo to next message
rhkoolstar is currently offline  rhkoolstar
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The 4008 lacks the second CE line (pin 30)
Re: Chipset based IBM PC/XT compatible 8088 board [message #3470 is a reply to message #3467] Tue, 19 September 2017 07:43 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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rhkoolstar wrote on Mon, 18 September 2017 23:41
The 4008 lacks the second CE line (pin 30)


Ha! I thought I stared at that schematic long enough that I should have noticed that. Casualty of being too late at night, I suppose.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3471 is a reply to message #3470] Tue, 19 September 2017 09:20 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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There is a spare inverter (U14a) that could be used to implement the second AS6C4008 by inverting
the address line A19 onto pin 22 of the 2nd AS6C4008, This would negate the need for the second
CE pin that the 1008 has (pin 30).

Sergey,

Once this design is mature (production version) I would be interested in a blank PCB.

regards

David Fry
Re: Chipset based IBM PC/XT compatible 8088 board [message #3472 is a reply to message #3467] Tue, 19 September 2017 09:31 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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rhkoolstar wrote on Mon, 18 September 2017 23:41
The 4008 lacks the second CE line (pin 30)


Yes, that was the reason for using 1008... But I naively assumed it has the same (TTL compatible) input voltage levels as 4008.

Unfortunately the chipset only generates RAM chip select for the first 640 KiB of RAM. So much of the second 4008 capacity won't be used. Of course it is possible to implement a separate chip select logic, either using discrete logic or an SPLD/GAL.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3473 is a reply to message #3471] Tue, 19 September 2017 09:35 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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dgf1966 wrote on Tue, 19 September 2017 09:20
There is a spare inverter (U14a) that could be used to implement the second AS6C4008 by inverting
the address line A19 onto pin 22 of the 2nd AS6C4008, This would negate the need for the second
CE pin that the 1008 has (pin 30).

That's an interesting idea. I'll test it on my prototype.

Quote:


Sergey,

Once this design is mature (production version) I would be interested in a blank PCB.

regards

David Fry


Sure
Re: Chipset based IBM PC/XT compatible 8088 board [message #3474 is a reply to message #3473] Tue, 19 September 2017 09:54 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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By the way, I am wondering what is the form factor you prefer in for the production board:

Options are:
1. Keep it an ISA 8-bit card (to be used with a backplane)
2. Motherboard - small form factor, e.g. similar to Mini ITX 17 × 17 cm (6.7' × 6.7'), with 5-6 ISA slots
3. Motherboard - Micro ATX -9.6" long, 6.7" or so wide - similar to my ISA Backplane, with 7-8 ISA slots
3. Motherboard - Baby AT format - 8.5" long, about 6.7" wide
Re: Chipset based IBM PC/XT compatible 8088 board [message #3475 is a reply to message #3474] Tue, 19 September 2017 10:02 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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My preference would either be ISA card (so it can directly replace the Xi 8088) or Micro-ATX (so it can directly replace the backplane + Xi 8088). Personally, I like the modularity of the ISA card, so that if/when someone comes out with an 80286 board or 80386sx board, we could easily swap to that.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3476 is a reply to message #3474] Tue, 19 September 2017 10:06 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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Sergey,

In order of preference my choice would be:-

1:- Micro ATX motherboard with however many slots will fit

2:- ISA 8-bit card

but if it comes down to cost I would be happy with the ISA 8-bit format


Regards

David Fry
Re: Chipset based IBM PC/XT compatible 8088 board [message #3552 is a reply to message #3476] Sat, 30 September 2017 08:52 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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Any news lately on experiences with the prototypes? I might have the opportunity where I could get a board fabricated for my own use, and I was curious if the design is sufficiently mature, or if there are expected revisions.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3555 is a reply to message #3552] Sat, 30 September 2017 12:53 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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smbaker wrote on Sat, 30 September 2017 08:52
Any news lately on experiences with the prototypes? I might have the opportunity where I could get a board fabricated for my own use, and I was curious if the design is sufficiently mature, or if there are expected revisions.

Scott


There is an issue with DMA, and I am working on a board revision with a fix.
Also there is a problem with AS6C1008 not having TTL compatible inputs.

More details:
DMA: Initially decided to save one 74ALS573 latch, assuming that DMA controller implemented in the chipset provides latched address lines. And I used a half of 74ALS244 to buffer A8-A11. So it turns out that chipset doesn't provide latched adresses. I am redesigning the board, adding that 74ALS573 back.
SRAM: The new revision will be using second AS6C4008 512 KiB SRAM for 512K-640K area. Also, I am planning to have a place for an optional SPLD that would implement UMBs using the rest of that SRAM.

Another update: I've modified my (Xi 8088) BIOS so it boots on Micro 8088 board. I still need to iron out a few small issues and see if I can implement a built-in setup utility for configuring floppy drive types.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3556 is a reply to message #3555] Sat, 30 September 2017 13:21 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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Awesome! Thanks for the update, and it's good to hear the Xi 8088 BIOS is now working on the board. I like that BIOS. ;) Did this resolve the V20 issues?

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3557 is a reply to message #3556] Sat, 30 September 2017 15:06 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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smbaker wrote on Sat, 30 September 2017 13:21
Did this resolve the V20 issues?


NEC V20 works just fine with my BIOS.
As I suspected the BIOS (from Intel Wildcard 88 board), which I used for the testing initially, doesn't work with NEC V20.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3609 is a reply to message #3557] Fri, 13 October 2017 21:13 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Hi,

I fixed a few issues from version 1.0, and re-designed the PCB. The new schematic and the PCB layout is attached. Please review Smile

Changes:

  • Added 74F573 latch to fix the DMA issue
  • Second SRAM changed to AS6C4008, 512 KiB part to fix the AS6C1008 TTL compatibility issue
  • Second SRAM chip select is implemented using two 74F00 gates
  • Added an option of using SPLD (ATF16V8B, GAL16V8) for SRAM address decode. This allows using available space in the second SRAM for UMBs
  • CLK and OSC signals are now buffered through 74F244 instead of a pair of 74*04 gates
  • Replaced 74ALS-series with 74F-series in the schematic and the PCB silkscreen. 74F are cheaper and faster (but 74ALS should work as well)
  • PCB rerouted to accommodate the new parts, some components re-arranged to (hopefully) shorten trace lengths.
  • PCB dimensions changed from 5"x4.3" to 6"x4" (152.4 mm x 101.6 mm). As the result the recommended ISA bracket changed to Keystone 9202.

Thanks,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3610 is a reply to message #3609] Fri, 13 October 2017 23:25 Go to previous messageGo to next message
andrii_kutepov is currently offline  andrii_kutepov
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Excellent, Sergey!!!

This chipset will work with you Trident ISA SVGA Card?

BR
Andrii
Re: Chipset based IBM PC/XT compatible 8088 board [message #3611 is a reply to message #3610] Sat, 14 October 2017 01:25 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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andrii_kutepov wrote on Fri, 13 October 2017 23:25
This chipset will work with you Trident ISA SVGA Card?


Yes, it works nicely with Trident TVGA9000i card. That's what I use for my tests and development. I actually have to try it with some other 8-bit compatible SVGA cards,but I don't expect any issues.

[Updated on: Sat, 14 October 2017 01:26]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3612 is a reply to message #3609] Sat, 14 October 2017 11:04 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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Hi Sergey,

Just a couple of observations:-)

Now that you have a GAL in the design would it not be logical to generate the RAMCS2 signal inside the GAL,
both RAMENA* and A19 are present on the GAL pins ?

This would eliminate 3 of the 4 gates in U14... The 4th gate is driving the speaker transistor Q1, you could
in theory just use 2 of the spare pins on the GAL to perform the inverter function therby doing away with U14 altogether
and giving youself a little more room in the top left corner of the PCB to play with.

On the subject of the SPKR signal from 14 of the FE2010A, does pin 14 rest low or high when no sound is being produced ?
If it rests low in its inactive state then no inverter is necessary, Q1 should only conduct when sound is being produced.

Best regards

David
Re: Chipset based IBM PC/XT compatible 8088 board [message #3613 is a reply to message #3612] Sat, 14 October 2017 11:11 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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Just one more observation,

Would it be a good idea to remove the GND connection from pin 3 of the speaker connector to prevent
the possibility of an incorrect jumper across pins 3-4 causing a direct short of the 5V rail.

For case speaker or the onboard sounder the GND connection would not be needed as the GND return for the
speaker/sounder is through Q1.

Regards

David
Re: Chipset based IBM PC/XT compatible 8088 board [message #3614 is a reply to message #3613] Sat, 14 October 2017 11:33 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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dgf1966 wrote on Sat, 14 October 2017 11:11
Would it be a good idea to remove the GND connection from pin 3 of the speaker connector to prevent
the possibility of an incorrect jumper across pins 3-4 causing a direct short of the 5V rail.


When I built up my Xi 8088, I just removed that pin from the header, after reading what happened to a couple of the other builders on Vogons.

An alternative would be to add provision for a PTC fuse or fusable link on the 5V line to that header. PTC on the keyboard would be nice too. I once killed a keyboard fuse on a 386 motherboard by playing around with a custom keyboard implementation. Had there been no fuse, I would have probably killed the motherboard.

dgf1966 wrote on Sat, 14 October 2017 11:11
Now that you have a GAL in the design would it not be logical to generate the RAMCS2 signal inside the GAL, both RAMENA* and A19 are present on the GAL pins ?


At first, I liked that the design is buildable without the GAL, as programmable logic often seems like mysterious black boxes to thwart my ability to understand and reverse engineer hardware that I find. That said, when I build one of these I'll probably include the GAL to get the UMB support anyway. I would think most people would choose to do this. Who doesn't want to make maximum use of that second 512K RAM chip?

Scott



[Updated on: Sat, 14 October 2017 11:37]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3616 is a reply to message #3612] Sat, 14 October 2017 12:52 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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dgf1966 wrote on Sat, 14 October 2017 11:04

Now that you have a GAL in the design would it not be logical to generate the RAMCS2 signal inside the GAL,
both RAMENA* and A19 are present on the GAL pins ?

This would eliminate 3 of the 4 gates in U14... The 4th gate is driving the speaker transistor Q1, you could
in theory just use 2 of the spare pins on the GAL to perform the inverter function therby doing away with U14 altogether
and giving youself a little more room in the top left corner of the PCB to play with.

On the subject of the SPKR signal from 14 of the FE2010A, does pin 14 rest low or high when no sound is being produced ?
If it rests low in its inactive state then no inverter is necessary, Q1 should only conduct when sound is being produced.


David, thank you for your feedback!

I did consider having an option of using either GAL (for UMB support) or 7400 (for 640 KiB), where GAL would do both address decode for the second SRAM and inverting the SPKR signal (yes, it does need to be inverted). That would have saved one 7400 IC when using GAL. I discarded this idea, because I was thinking it will complicate the switching between two configurations. Now looking at the schematic, it doesn't seem that it would complicate anything. So, I'll try to implement that.

Quote:

Would it be a good idea to remove the GND connection from pin 3 of the speaker connector to prevent
the possibility of an incorrect jumper across pins 3-4 causing a direct short of the 5V rail.


While what I have implemented follows the standard PC/AT implementation, I tend to agree with you. GND signal is normally not used there... Not even sure why it's needed (maybe to connect an external sound processing circuit?!Wink. In any case, if anyone will need that GND signal, it won't be difficult to solder a short wire between that pin and closed GND signal (e.g. on SW3).
Re: Chipset based IBM PC/XT compatible 8088 board [message #3617 is a reply to message #3614] Sat, 14 October 2017 12:58 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Hi Scott, and thank you for your feedback!

smbaker wrote on Sat, 14 October 2017 11:33

When I built up my Xi 8088, I just removed that pin from the header, after reading what happened to a couple of the other builders on Vogons.

An alternative would be to add provision for a PTC fuse or fusable link on the 5V line to that header.


Using a PTC for the speaker seems to be an overkill. Instead, I think about removing GND signal from SPEAKER connector altogether.

Quote:

PTC on the keyboard would be nice too. I once killed a keyboard fuse on a 386 motherboard by playing around with a custom keyboard implementation. Had there been no fuse, I would have probably killed the motherboard.


Makes sense, I'll see if I have a space on the PCB to add one.

Quote:

At first, I liked that the design is buildable without the GAL, as programmable logic often seems like mysterious black boxes to thwart my ability to understand and reverse engineer hardware that I find. That said, when I build one of these I'll probably include the GAL to get the UMB support anyway. I would think most people would choose to do this. Who doesn't want to make maximum use of that second 512K RAM chip?


It would be an option of using either GAL or 7400 (but without UMB). For creative folks, it is possible to replace that GAL with 2-4 logic ICs Smile
Re: Chipset based IBM PC/XT compatible 8088 board [message #3619 is a reply to message #3617] Mon, 16 October 2017 08:41 Go to previous messageGo to next message
etchedpixels is currently offline  etchedpixels
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Do you have enough space on the GAL to bank the extra space as EMM rather than or as well as UMB ? That way you could use all of it ?


Re: Chipset based IBM PC/XT compatible 8088 board [message #3620 is a reply to message #3619] Mon, 16 October 2017 10:39 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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etchedpixels wrote on Mon, 16 October 2017 08:41
Do you have enough space on the GAL to bank the extra space as EMM rather than or as well as UMB ? That way you could use all of it ?


EMS mapper won't fit in a SPLD. It would require a register file for memory mapping, including outputs for mapped addresses, data inputs, and I/O address decode logic to program that register file. The register file alone would need to have at least 20 bits of storage, the 16V8 SPLD only has 8 bits. While it is possible to use an external register file (e.g. a couple of 74LS670), that would further complicate the design.

Also, I find UMB to be more useful than a small amount of EMM. Newer DOS versions allow using UMBs for DOS buffers and to load device drivers, freeing up the base memory for applications.

If EMS is needed, I can suggest using this card.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3621 is a reply to message #3620] Mon, 16 October 2017 11:01 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Mon, 16 October 2017 10:39
While it is possible to use an external register file (e.g. a couple of 74LS670), that would further complicate the design.


How about a 74LS612? Hard to find these days, but for some reason I have one of those saved in my eBay watch list. I think I had some plan to implement EMS with it.

I like that you're keeping it simple with the Micro 8088. EMS on a separate board is a good solution.

skiselev wrote on Mon, 16 October 2017 10:39
If EMS is needed, I can suggest using this card.


These were unavailable for a while, but PCBs and finished boards have recently become available again! I only wish they were through-hole instead of SMD, as 90% of my retro build is through-hole.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3622 is a reply to message #3621] Mon, 16 October 2017 11:16 Go to previous messageGo to next message
etchedpixels is currently offline  etchedpixels
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I've seen the lo-tech card. The SMD put me off given I have enough trouble soldering normal sized objects. I've built some of their other stuff and been impressed with it.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3624 is a reply to message #3622] Mon, 16 October 2017 18:53 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Hi,

I made a few updates that we've discussed above:

1. Removed GND signal from the speaker connector
2. Connected keyboard voltage through a polyfuse
3. Used SPLD to generate /RAMCS2 and the inverted speaker signal

In addition I removed XSEL signal from SW2 DIP switch (replacing a 4 position DIP switch with a 3 position one), and added jumper JP4 instead. It is likely that this setting would need to be configured only once (depending on the crystal installed), and a simple wire bridge can be used.

I also updated the footprints for the DIP switches.

New schematic and PCB layout files are attached, please review.

Thanks,
Sergey

P.S. I rearranged SPLD pins a bit, freeing up pins 1 and 11 that can be used as Clock and /OE in SPLD registered mode. This gives some flexibility for using the currently unused SPLD pins. One possible use is an activity monitor (similar to what I've implemented in ISA backplane). In this case an address signal (e.g. A7) is connected to the Clock, pin 12 is programmed to change its state at each clock pulse, and pin 19, is programmed to be the inverse value of pin 12. A couple of LEDs connected to these pins will blink when board is running some code.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3626 is a reply to message #3624] Mon, 16 October 2017 23:49 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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Hi Sergey,

Quote:
3. Used SPLD to generate /RAMCS2 and the inverted speaker signal


U14 is still present on the PCB and in the schematic, it needs to be removed from the design
to complete the change

Regards

David Fry
Re: Chipset based IBM PC/XT compatible 8088 board [message #3627 is a reply to message #3626] Tue, 17 October 2017 07:11 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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dgf1966 wrote on Mon, 16 October 2017 23:49

U14 is still present on the PCB and in the schematic, it needs to be removed from the design
to complete the change


Hi David,

This is intentional. The design allows using either U14/74F00 or U16/ATF16V8B/GAL16V8 ICs. Some people might prefer to use 74F00, e.g. if they don't have a SPLD/GAL programmer, or prefer the simplicity of this approach.

Thanks,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3631 is a reply to message #3627] Wed, 18 October 2017 16:58 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Over last two day I rewired my version 1.0 board to test the changes for version 1.1.

It works great with either 74*00 or with SPLD. Had a few a bit scary moments, that turned to be nothing more than trivial errors in SPLD code (e.g. used logic AND instead of logic OR, or forgot to add decode for 0x80000-0x9FFFF addresses).

One thing which I've discovered by more carefully reading the FE2010 datasheet is that /EPSL signal used as the chip select for the EEPROM is activated for the entire 0xF0000-0xFFFFF area (not just for the upper 32 KiB as I hoped). This basically means that the 0xF0000-0xF7FFF is not usable for UMB. I think I'll rearrange the switches as follows:

SW3.1 - 0xC0000 - 0xC7FFF
SW3.2 - 0xC8000 - 0xCFFFF
SW3.3 - 0xD0000 - 0xD7FFF
SW3.4 - 0xD8000 - 0xDFFFF
SW3.5 - 0xE0000 - 0xEFFFF

Thanks,
Sergey

[Updated on: Wed, 18 October 2017 16:58]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3651 is a reply to message #3631] Tue, 24 October 2017 11:13 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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One more idea: Given that the available ROM space is actually 64 KiB, I am considering replacing the 28C256 EEPROM with the SST39SF010A Flash ROM. That IC is faster and cheaper, but has the disadvantage of not supporting byte reprogram. I was planning to use EEPROM to store the configuration (e.g. floppy drives types). It still should be doable with 39SF010 by using a 4 KiB page to store the configuration, and erasing/programming that page when configuration is updated. (This might not work with AM29F010B as it has bigger 16 KiB sector size, but should work with AT29C010A with smaller 128 bytes sector size)

When using a 128 KiB Flash ROM the A16 line would need to be tied LOW or HIGH. The easier way is just to tie it low, that way the Flash ROM could be programmed in system (the Flash ROM programming uses 0x2AAA and 0x5555 addresses). A slightly more complicated way is to have a jumper or a switch for the A16 line so it will be possible to switch between lower 64 KiB and upper 64 KiB. That would allow having alternate/backup BIOS image.

Any thoughts or suggestions about these modifications?
Re: Chipset based IBM PC/XT compatible 8088 board [message #3652 is a reply to message #3651] Tue, 24 October 2017 13:21 Go to previous messageGo to next message
will is currently offline  will
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Even better would be if A16 is normally under software control, granting easy software access to both lower and upper 64KB, so a software tool could easily flash both the main ROM and the "backup ROM" without the user moving any jumpers.

A board jumper could control whether A16 starts out as high or low (ie set the initial reset state of the flip-flop that drives A16) and thus allow the user to boot from either half of the ROM.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3653 is a reply to message #3652] Tue, 24 October 2017 13:49 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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will wrote on Tue, 24 October 2017 13:21
Even better would be if A16 is normally under software control, granting easy software access to both lower and upper 64KB, so a software tool could easily flash both the main ROM and the "backup ROM" without the user moving any jumpers.


Unfortunately, we don't have an available digital output that could be used to toggle A16.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3657 is a reply to message #3653] Wed, 25 October 2017 02:29 Go to previous messageGo to next message
will is currently offline  will
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Hmmm I wonder if one can be freed up somehow. Where can I find the datasheet for the FE2010A?
Re: Chipset based IBM PC/XT compatible 8088 board [message #3660 is a reply to message #3651] Wed, 25 October 2017 08:13 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Tue, 24 October 2017 11:13
Any thoughts or suggestions about these modifications?


I'm in favor of using the 39SF010 instead of the 28C256. I also think the jumper (or better yet, a switch), preferably in a location that could easily be accessed without having to remove the board, could be useful. Someone who doesn't care could just hardwire it to the lower 64K.

will
Even better would be if A16 is normally under software control, granting easy software access to both lower and upper 64KB...


Even better would be if we used a 39SF040 together with a banking scheme, and we could place DOS-in-ROM! Very Happy

Re: Chipset based IBM PC/XT compatible 8088 board [message #3662 is a reply to message #3657] Wed, 25 October 2017 09:20 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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will wrote on Wed, 25 October 2017 02:29
Hmmm I wonder if one can be freed up somehow. Where can I find the datasheet for the FE2010A?


The FE2010 (not FE2010A) datasheet is attached. As far as I know the difference between FE2010A vs. FE2010 is support for turbo modes (7.16 MHz, 9.5 MHz).
Re: Chipset based IBM PC/XT compatible 8088 board [message #3663 is a reply to message #3660] Wed, 25 October 2017 09:36 Go to previous messageGo to previous message
will is currently offline  will
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>Even better would be if we used a 39SF040

Scott -- yes certainly. 448KB for a ROM disk would be great.
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