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Re: Chipset based IBM PC/XT compatible 8088 board [message #3664 is a reply to message #3663] Wed, 25 October 2017 09:56 Go to previous messageGo to next message
will is currently offline  will
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Hmmm. I was going to suggest swapping PIC12F629 for PIC16F630, connecting the top 3 address bits of the ROM (and the reset line) to the PIC, and then send commands to the PIC over the keyboard interface for it to switch ROM banks. However now I remember the XT keyboard protocol is unidirectional, so that won't work because there's no way to get the command to the PIC. Shame.

Sadly I can't see a neat way to do it without adding more chips to the board for I/O address decoding and to latch the address bits.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3665 is a reply to message #3663] Wed, 25 October 2017 10:44 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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will wrote on Wed, 25 October 2017 09:36
>Even better would be if we used a 39SF040

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


Sounds like an idea for another project.... I've actually built something like this back in the day. As you can see PCB manufacturing services were not readily available that time Smile
Re: Chipset based IBM PC/XT compatible 8088 board [message #3666 is a reply to message #3664] Wed, 25 October 2017 11:44 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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will wrote on Wed, 25 October 2017 09:56
Hmmm. I was going to suggest swapping PIC12F629 for PIC16F630, connecting the top 3 address bits of the ROM (and the reset line) to the PIC, and then send commands to the PIC over the keyboard interface for it to switch ROM banks.


I think it's always a challenge in retro projects how much modern technology we incorporate. Using a PIC to translate keyboard protocol from XT to AT doesn't seem like a big deal, but implementing memory management using a PIC, even if it's something as simple as flipping the bit on an address line, seems like a bigger leap to me.

So there is no RTC on the Micro 8088? If an RTC and associated address decode (74hct138, etc) was added, then perhaps a spare output on that address decode could also be used to trigger a flipflop that could then control A16. There's something to be said for keeping the board simple though. I like that it's small.

skiselev
Sounds like an idea for another project.... I've actually built something like this back in the day. As you can see PCB manufacturing services were not readily available that time


I remember seeing that on your website and thinking it was cool! It does sound like a fun project.

I have a "BOCA Start Card" that I tried using with my Xi 8088 for a while, perhaps even before I build the floppy controller board. Still had DOS installed in the flash and booted right up. There was something funky with writing to the flash chips though, not only did it take forever, but the card would eventually start timing out on writes and turn out corrupted.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3667 is a reply to message #3666] Wed, 25 October 2017 14:14 Go to previous messageGo to next message
will is currently offline  will
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>There's something to be said for keeping the board simple though

Maybe you are right. A separate ISA card with several 512KB flash ROMs which can be banked into ISA memory is probably a better idea and it keeps the CPU board very simple.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3676 is a reply to message #3667] Thu, 26 October 2017 11:58 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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More food for thought: I checked the /EPSL signal generated by the chipset, that is used as the chip select for ROM, and, apparently it is only activated for memory read cycles (not memory write).

Because of this, the idea of modifying EEPROM / Flash ROM for configuration changes or in-system BIOS upgrades won't work. Unless, the ROM chip select will be generated in some another way, for example using SPLD.

So, there are two options:

  1. Do not support writing EEPROM / Flash ROM in the system. In this case, the design can be left as is, or the /MEMW and /MEMR signals can be disconnected altogether, and ROM's /OE tied to /LOW, and /WE tied HIGH (so that /CS used to read the ROM).
  2. Provide a way to use SPLD to generate chip select for the ROM. The SPLD already has all the required address lines, so only one additional output pit would be used. A jumper would be provided to select either SPLD or chipset as the ROM chip select source (in case people don't want to use SPLD).
Re: Chipset based IBM PC/XT compatible 8088 board [message #3677 is a reply to message #3676] Thu, 26 October 2017 12:38 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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I've never felt a need for in-system BIOS upgrades. I (and I assume other builders) have an external programmer that was needed in order to program the flash in the first place. If I need to re-flesh the BIOS, I just go back to that. The development cycle if you want to do BIOS development is more tedious since you have to physically move the chip.

Writing configuration does seem very useful though, almost a necessity. This brings me back to wishing you had a place on the board for the RTC, as the RTC has some nonvolatile RAM with it.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3683 is a reply to message #3676] Fri, 27 October 2017 09:38 Go to previous messageGo to next message
dgf1966 is currently offline  dgf1966
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I would tend to second Scotts observations,

In circuit reprogramming of ROM is not a big deal to me but it would be nice
to retain the DS12885 of the Xi8088 if possible, Even if it means the PCB
will be an inch longer.

You could make the DS12885 an optional extra which would require the use
of the 'optional' GAL16V8, or if there is not enough spare pins on that GAL
then a second GAL16V8 for DS12885 port decoding.
Or maybe just swap out both optional GAL16V8's for an optional GAL22V10.

A few options to consider Smile

regards


David
Re: Chipset based IBM PC/XT compatible 8088 board [message #3684 is a reply to message #3683] Fri, 27 October 2017 11:33 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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So far, the only necessary setting is going to be floppy drive types. There may be some optional settings, for example selecting the initial CPU clock frequency (normal, or one of two turbo frequencies).

The time keeping functionality is nice to have, but not really required. Back in 80's most of PC/XT's didn't have an RTC, and people lived happily without it Smile

It is not really possible to add DS12885/7 in Xi 8088 compatible way, this is because its I/O address will conflict with the chipset. It is possible to use another address (somewhere in 0x200-0x3FF range), but that won't be compatible with Xi 8088 or AT any more and likely will require a clock driver for DOS. Given that, and the additional complications of the board design (adding another SPLD and RTC components), I am a bit reluctant to this change.

Going back to the immediate issue at hand - floppy drive types and number configuration:
1. It should be possible to auto-detect the number of floppy drives on boot (seek to some track / seek to track 0), check if it is successful.
2. The actual floppy type can be auto-detected. For 2.88 MB (ED) and 1.44 (HD) floppy drives BIOS already does that, basically trying to read floppy ID at different speeds: 1 Mbps for 2.88 MB, 500 kbps for 1.44 MB, 250 kbps for 720 KB /360 KB. Might be a bit more difficult for 1.2 MB drives... does any one care about them though? Smile

For now, I think I'll stay with the current design. It should be fairly easy to mod to enable Flash ROM writes (cut the ROM CS trace, solder ROM CS to an available SPLD output, reprogram SPLD), in case people will want to do that.

[Updated on: Fri, 27 October 2017 11:51]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3685 is a reply to message #3684] Fri, 27 October 2017 16:13 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Fri, 27 October 2017 11:33
It is not really possible to add DS12885/7 in Xi 8088 compatible way, this is because its I/O address will conflict with the chipset.


Is the chipset intercepting addresses 70h and 71h where the RTC would normally be? I looked at the address map in the datasheet and didn't see anything there, but I don't know if this means the address space is free, or if the chipset has it aliased with some other peripheral.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3686 is a reply to message #3685] Fri, 27 October 2017 18:43 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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Need to verify that the chipset is fully decoding the addresses, and won't write the PPI for example (like it would do on an original XT, that only decodes A9-A5 for I/O ports, and ignores A4-A0).
Another potential issue is the DTR (direction) signal for data bus transceiver - U10 on the schematic. I am assuming that for I/O read operations from 0x00-0xFF port range the direction of that transceiver is going to be from the CPU/chipset to the ISA bus, while if using RTC (connected to the ISA bus), we'll want to have the opposite direction (from the ISA to the CPU/chipset). It might be that chipset designers were smart, and the chipset only changes the direction for the read operation for valid addresses, but I doubt that ;-)

I can try testing it all, but as I said before, I see a little benefit of implementing RTC but a lot of hassle.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3688 is a reply to message #3686] Fri, 27 October 2017 20:15 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Fri, 27 October 2017 18:43
I see a little benefit of implementing RTC but a lot of hassle.


Yeah, I hear where you're coming from. My first x86 PC didn't have a RTC either, and it's not like I need accurate time of day in my retro computer...

Besides, it'll give one of us the opportunity to build a RTC board! (assuming the chipset does not cause problems)
Re: Chipset based IBM PC/XT compatible 8088 board [message #3707 is a reply to message #3688] Wed, 01 November 2017 16:02 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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I added a connection between /ROMCS and a previously unused SPLD pin, so that the SPLD can be used to generate this signal. I also added a jumper JP4 to connect /ROMCS to chipset's /EPSL signal in case the SPLD is not used.

And with that modification, I've placed the order for PCBs version 1.1.

If everything goes well I should have the PCBs in about three weeks from now.

Meanwhile I'll try to allocate time to work on the BIOS fixes.

I uploaded the design files to the GitHub repository, but I didn't have time to update the documentation yet.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3708 is a reply to message #3707] Wed, 01 November 2017 18:44 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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Excellent news! I'm looking forward to hearing how they work out. Are you expecting to have them available for sale any time soon?

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3709 is a reply to message #3708] Wed, 01 November 2017 22:57 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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smbaker wrote on Wed, 01 November 2017 18:44
Excellent news! I'm looking forward to hearing how they work out. Are you expecting to have them available for sale any time soon?


Once I get the PCBs from the manufacturer, I'll build and test one (as soon as I can). If it works to my satisfaction, I'll be offering PCBs for sale.

The estimated PCB price is going to be $15 + shipping, and I'll have some FE2010A chips for $10 each.

Thanks,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3710 is a reply to message #3709] Thu, 02 November 2017 04:49 Go to previous messageGo to next message
andrii_kutepov is currently offline  andrii_kutepov
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Sergey,

Me interest for pcb and chips.

Thanks
Andrii
Re: Chipset based IBM PC/XT compatible 8088 board [message #3712 is a reply to message #3709] Thu, 02 November 2017 08:56 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Wed, 01 November 2017 22:57
Once I get the PCBs from the manufacturer, I'll build and test one (as soon as I can). If it works to my satisfaction, I'll be offering PCBs for sale.


Excellent. If there's a wait list or interest list, please add me. ;) I already have everything I need (including the FE2010), just need a PCB! Anxiously looking forward to this one, and thanks for all the work you've put into it.

scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3720 is a reply to message #3712] Thu, 09 November 2017 00:18 Go to previous messageGo to next message
andrii_kutepov is currently offline  andrii_kutepov
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I'm not sure what this news for this topic, but may be interesting for builders new XT computers.
On russian forum some guys discovered problem why SVGA Card from Sergey don't work on XT and on russian clone with 8086 CPU Poisk-2.
Problem with ALE signal:
Addition info and solution on russian forum from this link:
http://www.phantom.sannata.ru/forum/index.php?t=27064&p= 403378#pp403378

[Updated on: Thu, 09 November 2017 00:18]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3721 is a reply to message #3720] Thu, 09 November 2017 07:23 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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Hi Andrii,

Yes, I saw that post.
There is another conversation on this topic here:
http://www.vcfed.org/forum/showthread.php?39291-Trident-VGA- and-IBM-PC

Thanks,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3831 is a reply to message #3721] Thu, 23 November 2017 15:26 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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I am pleased to announce that I've received Micro 8088 boards from the manufacturer and I am ready to distribute them. I also have several Faraday FE2010A ICs. Please see Board Inventory page for the ordering information.

Yesterday evening I've built and tested one board in a few different configurations:
- With and without the SPLD
- Using 14.31818 MHz and 28.63636 MHz crystals
- Intel P8088-2, Intersil CP80C88, NEC V20 CPUs, and Intel D8087-1 FPU. All work nicely at 9.54 MHz (4.77 MHz and 7.16 MHz works too)
- 512 KiB and 1 MiB SRAM (UMB configuration with SPLD)
- I tested the board using 74F-series buffers/latches/transceivers. And I will be testing other logic families as time allows.

The BIOS still needs a few improvements. But generally it works OK.

The Micro 8088 project information is currently hosted in this GitHub repository.

- Sergey

[Updated on: Thu, 23 November 2017 15:48]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3832 is a reply to message #3831] Fri, 24 November 2017 03:54 Go to previous messageGo to next message
andrii_kutepov is currently offline  andrii_kutepov
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Hi, Sergey

I want to reserve 1 pcb "Micro 8088" and 2 chips, but still wait 8088-FE2010A-SBC-Board for combine shiping.
Also me need some other boards from 8088 project, who sells Todd.
Thanks

Andrii
Re: Chipset based IBM PC/XT compatible 8088 board [message #3846 is a reply to message #3832] Mon, 27 November 2017 10:24 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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Sergey,

Where do I find the BIOS and the firmware for the PIC? Do I use the most recent Xi 8088 BIOS?

Thanks,
Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3847 is a reply to message #3846] Mon, 27 November 2017 10:40 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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smbaker wrote on Mon, 27 November 2017 10:24

Where do I find the BIOS and the firmware for the PIC? Do I use the most recent Xi 8088 BIOS?


Micro 8088 uses AT2XT PIC firmware, which is available here: http://www.vcfed.org/forum/showthread.php?26426-AT2XT-keyboa rd-converter

I still need to put the BIOS on the GitHub, will try to do it this evening.

[Updated on: Mon, 27 November 2017 10:40]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3848 is a reply to message #3847] Mon, 27 November 2017 10:59 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Mon, 27 November 2017 10:40
I still need to put the BIOS on the GitHub, will try to do it this evening.


Thanks Sergey, Much appreciated. I think my hardware is built. The board looks really nice!

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3856 is a reply to message #3848] Tue, 28 November 2017 08:26 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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It's working with this morning's BIOS!

Well, at least mostly working. I'm having a few small issues:

1) Direct connecting a keyboard works fine, but my KVM-IP does not work. Unsure why, probably need to start by checking to make sure the KVM-IP is still working correctly and its cable is good.

2) CTRL-ALT-DEL will cause it to fail to boot from compactflash.

3) I have a TSR that I run on startup that steals int 1c. It works fine on the xi 8088 but doesn't work right on the micro 8088, and causes other programs to not work right too. This could be my fault, when I get a chance I will figure out what part of the program is triggering the bad behavior.

How do I get it to run at speeds > 4.77 MHz? Do I need to write port 63h bits 6 or 7 myself?

It's currently sitting here running checkit, set for 100 memory test passes. So far seems to be working well. I'll let it burn in while I'm at work.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3857 is a reply to message #3856] Tue, 28 November 2017 09:04 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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smbaker wrote on Tue, 28 November 2017 08:26
It's working with this morning's BIOS!


Cool! Thank you for testing

Quote:

1) Direct connecting a keyboard works fine, but my KVM-IP does not work. Unsure why, probably need to start by checking to make sure the KVM-IP is still working correctly and its cable is good.


I am unsure why this is happening. It might be some incompatibility between your KVM and AT2XT firmware. Perhaps worth checking and/or asking at the AT2XT thread here

Quote:

2) CTRL-ALT-DEL will cause it to fail to boot from compactflash.


I am aware of this issue. It looks that something in the BIOS data area does not get initialized on warm reset. This is the top item on my to do list

Quote:

3) I have a TSR that I run on startup that steals int 1c. It works fine on the xi 8088 but doesn't work right on the micro 8088, and causes other programs to not work right too. This could be my fault, when I get a chance I will figure out what part of the program is triggering the bad behavior.


The IRQ0 / INT 8 / INT 1C logic shouldn't have changed, or at least I don't remember changing anything there. Is it possible that your program misbehaves because of some another issue? (for example, the keyboard code changed quite a bit, and it is not near to be well debugged)

Quote:

How do I get it to run at speeds > 4.77 MHz? Do I need to write port 63h bits 6 or 7 myself?


Currently you'll need to do that manually, but it is the next item on the to do list Smile

Run "debug", and use the following commands to change the CPU clock:
- To set normal/default 4.77 MHz CPU clock: "o 63 01" without FPU, or "o 63 03" with FPU
- To set 7.15 MHz CPU clock: "o 63 41" without FPU, or "o 63 43" with FPU
- To set 9.55 MHz CPU clock: "o 63 81" without FPU, or "o 63 83" with FPU

Alternatively, you can write a really short program to out these values to port 63h.

Thanks,
Sergey

[Updated on: Tue, 28 November 2017 09:05]

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Re: Chipset based IBM PC/XT compatible 8088 board [message #3858 is a reply to message #3857] Tue, 28 November 2017 09:38 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Tue, 28 November 2017 09:04
The IRQ0 / INT 8 / INT 1C logic shouldn't have changed, or at least I don't remember changing anything there. Is it possible that your program misbehaves because of some another issue? (for example, the keyboard code changed quite a bit, and it is not near to be well debugged)


I forgot that my TSR uses the RTC... So that explains the aberrant behavior.

skiselev wrote on Tue, 28 November 2017 09:04
Alternatively, you can write a really short program to out these values to port 63h.


I was thinking of doing that when I get off work tonight. Should only be a few minutes work.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3867 is a reply to message #3858] Tue, 28 November 2017 21:07 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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My keyboard issue turned out to be a cable problem. I trimmed a bit off the plastic molding on the male connector, so that it fits into the socket a bit deeper, and all is well with the KVM.

Question about power-on reset. It looks like the reference design in the FE2010A datasheet has a 470 ohm resistor from !REST to VCC, whereas the Micro 8088 instead has the 470 ohm resistor from !REST to the reset switch and header. Why? Isn't that RC combination necessary to generate power-on reset?

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3868 is a reply to message #3867] Tue, 28 November 2017 22:09 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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smbaker wrote on Tue, 28 November 2017 21:07

Question about power-on reset. It looks like the reference design in the FE2010A datasheet has a 470 ohm resistor from !REST to VCC, whereas the Micro 8088 instead has the 470 ohm resistor from !REST to the reset switch and header. Why? Isn't that RC combination necessary to generate power-on reset?

Both Micro 8088 and the FE2010A reference design have an RC reset circuit with 10 kohm resistor and 10 uF capacitor. The difference is that Micro 8088 adds a 470 ohm resistor between the reset switch and 10 uF capacitor. This resistor limits the current flowing through the reset switch when it is pressed to less than 10 mA, prolonging the life of that switch. Without the resistor, the switch basically short circuits the capacitor, resulting in momentary high current.

Meanwhile I did a few updates to the BIOS:
- I added turbo mode switch functionality, it uses Ctrl-Alt-Keypad{-|*|+} for 4.77 MHz, 7.16 MHz, and 9.55 MHz CPU frequency respectively
- I think I fixed the XT-IDE BIOS extension not working after Ctrl-Alt-Del issue. It is a fairly stupid problem: XT-IDE BIOS will not initialize if Ctrl button is pressed, and apparently keyboard was not reset and keyboard buffer was not flushed when system was rebooted using Ctrl-Alt-Del

I am planning to post the updated BIOS on GitHub later tonight.
Re: Chipset based IBM PC/XT compatible 8088 board [message #3869 is a reply to message #3868] Tue, 28 November 2017 22:23 Go to previous messageGo to next message
smbaker is currently offline  smbaker
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skiselev wrote on Tue, 28 November 2017 22:09
Both Micro 8088 and the FE2010A reference design have an RC reset circuit with 10 kohm resistor and 10 uF capacitor.


Thanks Sergey, took me a while to spot it over there on RR2.

Scott
Re: Chipset based IBM PC/XT compatible 8088 board [message #3911 is a reply to message #3869] Thu, 07 December 2017 13:14 Go to previous messageGo to next message
skiselev is currently offline  skiselev
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Meanwhile I was working on the BIOS updates.
I've published version 0.9.4 earlier today.

There are multiple fixes and improvements since the original, version 0.9.2, such as:

- Built-in BIOS setup utility that allows configuring floppy drive types and storing the configuration to the Flash ROM
- Turbo switching using <Ctrl>-<Alt>-<+>, <Ctrl>-<Alt>-<*>, and <Ctrl>-<Alt>-<->
- Multiple bug fixes

Thanks,
Sergey
Re: Chipset based IBM PC/XT compatible 8088 board [message #3920 is a reply to message #3402] Sun, 10 December 2017 16:59 Go to previous messageGo to next message
Wayne W is currently offline  Wayne W
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Hi Sergey,

Just finished building two of these. Went very smoothly and both boards are working perfectly.

The only struggle I had was getting my PICs programmed. For some reason, my programmer did not get them programmed properly even though it said it did and verified them. After using my older programmer, they worked perfectly.

Thanks for this nice project Sergey.

-Wayne
Re: Chipset based IBM PC/XT compatible 8088 board [message #3922 is a reply to message #3920] Sun, 10 December 2017 17:22 Go to previous message
smbaker is currently offline  smbaker
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After some initial struggles which I think turned out to be related to my choice of CompactFlash card in the XT-CF-Lite, my Micro 8088 system is solid and stable.

Thanks Sergey for this project, it has been a fun build!

Now we just need to talk Sergey into designing an 80286 SBC. Very Happy

Scott
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