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8085 SBC [message #2280] Fri, 07 April 2017 17:08 Go to next message
Sergey is currently offline  Sergey
Messages: 120
Registered: October 2015
Location: Portland, OR
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Hi,

I've designed and built a very simple 8085 SBC. It might be good as a first homebrew computer project, and for learning how microcomputers work.

The documentation is here:
http://www.malinov.com/Home/sergeys-projects/minimax8085

Some future plans (when I have time):
- Port Tiny BASIC to this SBC, to be programmed in the EPROM
- Design a CP/M board for it - featuring a permanent storage device, and some paged RAM.

Anyone interested in getting and building this board? If so, I'll order some PCBs. I can also get and program some SPLDs (althought they can be easily programmed using common MiniPro TL866 programmer).

Regards,
Sergey
Re: 8085 SBC [message #2283 is a reply to message #2280] Fri, 07 April 2017 22:03 Go to previous messageGo to next message
Wayne W is currently offline  Wayne W
Messages: 282
Registered: October 2015
Location: Fountain Valley, Californ...
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Hi Sergey,

Interesting project. I would definitely like a couple of these boards.

-Wayne
Re: 8085 SBC [message #2285 is a reply to message #2283] Fri, 07 April 2017 23:19 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Sergey,
I have never had an 8085 SBC. It would be interesting. I'd like a couple boards please. Thanks a bunch.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2286 is a reply to message #2280] Sat, 08 April 2017 00:03 Go to previous messageGo to next message
mscane is currently offline  mscane
Messages: 102
Registered: October 2015
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HI Sergey,

Looks like an interesting project. I would be interested in two boards.

To bring up CP/M you will need to get the ROM out of the address space and replace it with RAM.

Perhaps the SWAP_MEM signal could become a ROM_DISABLE signal? That way you could add memory on a second board and switch it in via an i/o port.

Or perhaps disable both the main board RAM and ROM and implement an MMU on the second board like the Zeta V2?

Lots of possibilities.

Cheers!

Max
Re: 8085 SBC [message #2293 is a reply to message #2286] Sat, 08 April 2017 10:00 Go to previous messageGo to next message
pbirkel is currently offline  pbirkel
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Registered: October 2015
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Sergey: Please add me to the list for two PCBs. I'd be interested in a pair of programmed SPLDs as well. And, there's never enough time. Worse than real estate ...
Re: 8085 SBC [message #2301 is a reply to message #2286] Sat, 08 April 2017 12:24 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 120
Registered: October 2015
Location: Portland, OR
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Max,

Quote:
To bring up CP/M you will need to get the ROM out of the address space and replace it with RAM.

Perhaps the SWAP_MEM signal could become a ROM_DISABLE signal? That way you could add memory on a second board and switch it in via an i/o port.

Or perhaps disable both the main board RAM and ROM and implement an MMU on the second board like the Zeta V2?

SWAP_MEM signal is connected to the SPLD, and it is definitely possible to program it to disable ROM or to disable both ROM and RAM.

My hope was that it would be possible to put a small CP/M image in 32 KiB ROM, and then have a really simple extension board - I/O address decode + D latch (might be just another SPLD) to control the SWAP_MEM signal.

Thanks,
Sergey
Re: 8085 SBC [message #2308 is a reply to message #2301] Sat, 08 April 2017 15:34 Go to previous messageGo to next message
mscane is currently offline  mscane
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Registered: October 2015
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skiselev wrote on Sun, 09 April 2017 05:24

My hope was that it would be possible to put a small CP/M image in 32 KiB ROM, and then have a really simple extension board - I/O address decode + D latch (might be just another SPLD) to control the SWAP_MEM signal.



It is definitely do-able. The minimum RAM for CP/M 2.2 is 20 KiB if I remember correctly. Putting most of your BIOS into ROM will help a lot. However, the data structures required for each CP/M drive will require RAM. Also depending on what type of disk you use (SD, CF etc) you will probably need a 512 byte de-blocking buffer.

Large programs such as Wordstar and MBasic might not run that well in such a small TPA.

For a 64 KiB system all you would need is a second 32 KiB ram on the expansion board which replaces the ROM based on an I/O port that drives the ROM_DISABLE. At boot up copy the code from ROM to High RAM and then switch in the lower RAM. That give you an all RAM address space.

Adding a CF disk in 8 bit mode would just require a connection to the data bus, control signals and two CS signals. The PAL should be able to handle all that I think.

Of course the other challenge would be stopping myself using Z80 instructions such as LDIR and DJNZ... Smile

Cheers!

Max

Re: 8085 SBC [message #2317 is a reply to message #2308] Sun, 09 April 2017 10:26 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
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Registered: November 2015
Location: Chapin, SC
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I actually have an 8085 chip or two lying around with no home, and this looks like a fun project, so I'm game for two boards.

Dave London
Re: 8085 SBC [message #2323 is a reply to message #2317] Sun, 09 April 2017 14:27 Go to previous messageGo to next message
gkaufman is currently offline  gkaufman
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Registered: October 2015
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Two PC boards for me as well please.
Lots of spare 8085's looking for a use Smile

- Gary
Re: 8085 SBC [message #2354 is a reply to message #2323] Mon, 10 April 2017 15:36 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
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1 board for me please
Re: 8085 SBC [message #2375 is a reply to message #2354] Thu, 13 April 2017 09:09 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 120
Registered: October 2015
Location: Portland, OR
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Cool, a lot of interest! I ordered the PCBs, and I should have them back in about a month.

Meanwhile I made TinyBASIC 2.0 run on my board. That was pretty easy - just a few USART and memory configuration updates. I posted the details and the TinyBASIC source and binary image on the project page.
A bit more challenging thing would be to make TinyBASIC live together with MON85 in the same ROM. It looks like both use RST instructions, and so their code starts from 0000h. It should be possible to replace RST with CALL in the BASIC. It would slightly increase the resulting code size, but it shouldn't be a problem, since the ROM size is at least 8 KiB.
Re: 8085 SBC [message #2577 is a reply to message #2375] Sun, 30 April 2017 10:45 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Registered: October 2015
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The 8085 PCBs had arrived from the manufacturer. They are $5 each, plus shipping - $3 in USA, $15 overseas.
If you're interested, please PM me or e-mail at skiselev <at> gmail <dot> com

Thanks,
Sergey
Re: 8085 SBC [message #2659 is a reply to message #2577] Sat, 06 May 2017 16:24 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Guys,
I am in need of a couple of 80C85A cpu chips. If anyone has a couple of spare chips, please let me know. I have 2 boards so I am beginning to populate one. Thanks a bunch! Take care my friends.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2660 is a reply to message #2659] Sat, 06 May 2017 16:29 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Sergey,
I have never seen 3 pin caps so I'm wondering how I should install my 0.1uf and 1uf caps with 0.1 lead spacing. Thanks a bunch.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2661 is a reply to message #2660] Sat, 06 May 2017 17:06 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
Messages: 41
Registered: November 2015
Location: Chapin, SC
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Hi Kip,

I believe the caps are laid out to accommodate both 0.1" and 0.2" spaced caps. Two of the three pads (center and one side) are common and the other is the shared lead. You can verify this with a meter and check continuity. You'll see two pads are connected to each other and the third is not. The 0.2" spaced caps are obviously installed into the outer pads. If you are installing a 0.1" spaced cap, you need to make sure to choose the non-connected pads.

Dave
Re: 8085 SBC [message #2662 is a reply to message #2661] Sat, 06 May 2017 18:29 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 120
Registered: October 2015
Location: Portland, OR
Senior Member
Dave is mostly correct. I use the 3 pin capacitor footprints for MAX232 charge pump capacitors. Some MAX232 types use 1uF capacitors, and these 3-pin footprints allows using electrolytic capacitors with 1.8 mm - 2.5 mm lead spacing for such MAX232 ICs using the outer hole marked with (+) sign and the middle hole. Other MAX232 compatible ICs (MAX202, MAX232A) can work with 0.1uF capacitors, and ceramic capacitors with 5 mm (0.2") lead spacing can be installed then using outer holes.

[Updated on: Sat, 06 May 2017 18:30]

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Re: 8085 SBC [message #2664 is a reply to message #2662] Sat, 06 May 2017 19:57 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Guys,
Thanks so much for the pointers. I should have guessed that.
Now another question. I'm trying to find the datasheet for the OKI M80C85A-2 chip I found on ebay.
< http://www.ebay.com/itm/OKI-M80C85A-2-8-BitCMOS-MICROPROCESS OR-/401213617674?hash=item5d6a31f60a:g:LJ4AAOSwB09YD3aX>
Is this the fastest version of the chip? It certainly is the cheapest I've found so far from a US seller.
If anyone has a nice fast 80C85A chip laying around, I certainly would like to get a couple of those as well.
Both should be DIPs style for Sergey's 8083 SBC. Any pointers obtaining these chips is most appreciated.
Thanks in advance.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2665 is a reply to message #2664] Sat, 06 May 2017 20:06 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
Senior Member

Hi Guys,
All I'm finding on ebay right now for the 80C85A is M80C85A-2 chips and for the 82C51A is M82C51A-2 chips. What is the speed of these chips?
I can't locate a M80C85A-2 datasheet. I haven't looked for the M82C51A-2 datasheet yet.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2668 is a reply to message #2280] Sat, 06 May 2017 21:23 Go to previous messageGo to next message
Andrew B is currently offline  Andrew B
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Registered: October 2015
Location: Hawthorne, CA
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Jameco has 8085s, no need to resort to eBay....

3mhz - http://www.jameco.com/webapp/wcs/stores/servlet/ProductDispl ay?productId=52062
5mhz - http://www.jameco.com/webapp/wcs/stores/servlet/ProductDispl ay?productId=52071

Looks like there are 6mhz HMOS parts too. Sergey talks about the different speed grades (- numbers) on this site:

Quote:

80C85 (CPU) - Any type in DIP-40 package will do. Use 6.144 MHz crystal for 3 MHz parts. Such parts usually don't have any numeric suffix in the part name. For example Intel P8085AH is a 3 MHz part, while Intel P8085AH-2 is a 5 MHz part.
CMOS parts: MSM80C85A or M80C85A (OKI), CA80C85B (Calmos, Tundra), IM1821VM85A (Soviet/Russian Clone)
NMOS parts: P8085A (Intel, AMD), P8085AH, P8085AH-2, P8085AH-1 (Intel, newer HMOS process, 3 MHz, 5 MHz, and 6 MHz parts respectively), M5L8085AP (Mitsubishi), TMP8085AP (Toshiba), and so on.

Re: 8085 SBC [message #2669 is a reply to message #2665] Sat, 06 May 2017 21:36 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 120
Registered: October 2015
Location: Portland, OR
Senior Member
Clock frequencies for various 8085 CPUs:
NMOS, Intel and other vendors:
8085A/8085AH - 3 MHz
8085AH-2 - 5 MHz
8085AH-1 - 6 MHz
CMOS, OKI:
MSM80C85A - 3 MHz
MSM80C85A-2 - 5 MHz
MSM80C85AH - 5 MHz
CMOS, CALMOS/Newbridge/Tundra:
CA80C85B-X, where X is the clock frequency

Notes:
- You can always run a faster CPU at lower frequency
- 8085 SBC uses the CPU clock frequency for USART. It gets divided by SPLD to obtain 307.2 kHz and 153.6 kHz. I provided SPLD fuse maps (images) to divide the clock by 10/20 and 16/32 for 3.072 MHz and 4.9152 MHz CPU clock respectively​. The SPLD might need to be reprogrammed for other CPU clock frequencies. In case of 6 MHz CPU it should be possible to use 6.144 MHz clock (12.288 MHz crystal) and 3.072 MHz SPLD fuse map. This will result in doubled UART bit rate (e.g. 19200 bps instead of 9600 bps).
If there is an interest, I can develop divide by 12/24 SPLD image to use with 14.7456 MHz crystals / 7.3728 MHz CPU clock. This seems to be the closest readily available frequency to 8 MHz. (15.9744 MHz crystal / 7.9872 MHz CPU with divide by 13/26 is even closer, but these crystals are rare)

[Updated on: Sat, 06 May 2017 22:24]

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Re: 8085 SBC [message #2671 is a reply to message #2669] Sun, 07 May 2017 08:41 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
Messages: 41
Registered: November 2015
Location: Chapin, SC
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UTSource has the CA80C85B-8CP parts listed on eBay for $4 each (plus $2 shipping). I just ordered several to test. These should be the 8MHz CMOS 40 pin DIP parts.
Re: 8085 SBC [message #2675 is a reply to message #2671] Sun, 07 May 2017 11:47 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Andrew B, Sergey & Dave!
Thanks a Bunch for the heads up! I just bought a few of them. This is the url I used.
< http://www.ebay.com/itm/1PCS-CA80C85B-8CP-Encapsulation-DIP- TRANSIL-/381034166826?hash=item58b767fa2a:g:4g0AAOSwc0FUo~3D>
It matches the details the message. Now I have to figure out the correct master clock crystal frequency.
I suppose I will get all the appropriate crystals from 3.072MHZ on up. Smile Thanks very much! Take care my friend.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2676 is a reply to message #2675] Sun, 07 May 2017 15:45 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
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Registered: November 2015
Location: Chapin, SC
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I just purchased some 15.9744MHz crystals in the HC-49S package on ebay. They are SMD packages, but if they are like the other SMD HC-49S crystals I've seen, you can bend the pins down and use them as through hole pins.

I bought a 10 pack, so if they will work, I'd be happy to send the rest out to those that want them. They also have 9 more 10 packs still for sale at $5.25 and free shipping. Search for 112365126435.

[Updated on: Sun, 07 May 2017 15:45]

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Re: 8085 SBC [message #2677 is a reply to message #2676] Sun, 07 May 2017 17:29 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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It struck me this morning that 16 MHz crystal is close enough to 15.9744 MHz for USART operation (just 0.16% off). I found one of these crystals and going to try it later today.
Re: 8085 SBC [message #2678 is a reply to message #2677] Sun, 07 May 2017 23:02 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Registered: October 2015
Location: Portland, OR
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I uploaded the updated Mini8085-SPLD-1.2.zip file with SPLD fuse maps. Now it includes Mini8085-3.9936MHz.jed fuse map that divides the CPU clock by 13 and 26. I tested it, and it works just fine with 8 MHz Tundra CA80C85B-8CP CPU using 16 MHz crystal. In this case USART clock is doubled, so I get 38400 bps bit rate when the JP3 in 19200 bps position. I am using OKI M82C51A-2 USART, and it appears to work just fine with 8 MHz clock and 38400 bps bit rate.
Re: 8085 SBC [message #2679 is a reply to message #2678] Sun, 07 May 2017 23:32 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Sergey,
Thank you for checking this out and updating the zip file. I can now get the crystals. I appreciate your work.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2953 is a reply to message #2679] Sun, 04 June 2017 09:11 Go to previous messageGo to next message
gkaufman is currently offline  gkaufman
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Board went together easily. I'm using older CPU's so stuck with 6.144mhz xtal.

Both the monitor and Tiny Basic run nicely.

Sergey, thanks again for a cute little project. Hope you find time for a CP/M board.

- Gary
Re: 8085 SBC [message #2963 is a reply to message #2953] Mon, 05 June 2017 10:15 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Location: Portland, OR
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Gary,

I am glad your board works fine, and I appreciate your the feedback.

Max Scane is working on a CP/M extension card, with some additional page-able memory, storage, and a 8255 PPI.

Thanks,
Sergey
Re: 8085 SBC [message #2965 is a reply to message #2280] Mon, 05 June 2017 12:12 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
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Sergey,

My experience was similar to Gary's. I built two boards, one with a regular Intel 8085 chip and the other with a Tundra 8MHz CPU. The Intel came up first try, but the Tundra was sending garbled data. I finally realized I had written the wrong JED file to the GAL. Once I switched it out, that one came up fine at 8MHz.

I look forward to Max's CP/M extension project.

Dave London
Re: 8085 SBC [message #2966 is a reply to message #2965] Mon, 05 June 2017 13:09 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Sergey,
With the extension CP/M board on the design board, is there a possibility that this 8085 SBC will be able to run Altair disk based software?
Will the extension board have more serial ports on it?
Max, what is the feature list you are looking at including on the extension board?


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #2971 is a reply to message #2966] Mon, 05 June 2017 19:05 Go to previous messageGo to next message
mscane is currently offline  mscane
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It is at the concept stage at the moment however, I would like to have the following:

1. Bus connected Compact flash card (8 bit mode)
2. Bit Banged SD card
3. 512 KB RAM as banked RAM (in lower 32KB)
4. 8255 PPI (PLCC) for external devices.

The 512KB RAM might be a bit of over kill but it takes up the same space as two 32KB RAMs in narrow DIP.

32KB common with two 32KB banks is sufficient for CP/M 3 and the remaining RAM could be used as a RAM disk.

Board space is tight but I should be able to implement it with an 8 bit register (74LS273), an input buffer (74LS125) and a GAL for glue. The GAL on the CPU board will need a small change to make the swap_ram signal operate as a ROM_disable signal allowing the 512KB RAM to respond to the lower 32KB address space.

The register will hold the upper address lines, SD card signals and ROM_disable signal. The input buffer would have the SD card MISO, CD and WP along with a single jumper maybe.

The CF card should be reasonably fast as it is bus connected. The SD card will be slower as it is bit banged. I liken it to hard disk vs floppy. Both have their uses and together would make a nice little CP/M computer.

Suggestions/comments welcome!


Cheers!

Max

Re: 8085 SBC [message #3011 is a reply to message #2971] Wed, 07 June 2017 11:35 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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I've got the new batch of MiniMax8085 PCBs from the manufacturer, and added the information on the board inventory page.
I also copied the MiniMax8085 documentation to the Wiki.

Thanks,
Sergey
Re: 8085 SBC [message #3018 is a reply to message #3011] Thu, 08 June 2017 05:31 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
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Hi Max,
You are a tireless software and hardware designer! Thank you for your continued efforts!
Is there a possibility that the extension board could be made to run Altair code unaltered?


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #3024 is a reply to message #3018] Thu, 08 June 2017 09:20 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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Registered: October 2015
Location: Portland, OR
Senior Member
Kip,

Can you elaborate on what Altair code you want to run? Is it CP/M programs?
8085 is backward compatible with 8080 used in Altair, so the code by itself would run, with a few caveats:
1. Operating environment: For example: CP/M, BIOS, BASIC, etc. If I am not mistaken the original Altair was shipped with no ROM at all. Many users upgraded their system later on to add disk support, CP/M, possibly including the BIOS in a ROM.
2. Memory size and mapping: The original Altair had something like 256 bytes of memory... not exceptionally useful. Again, many users added more memory. In case of Altair, RAM starts at 0000h. In case of 8085 SBC, RAM starts at 8000h (it is possible to remap the memory). Either the software needs to be modified to run from 8000h, or an extension board can be used to put RAM at 0000h. The CP/M board Max mentioned would do that.
3. I/O devices. Original Altair came with no I/O (except of blinky LEDs and switches on the front panel, that are not exactly I/O). Many users added devices, such as UARTs, disk controllers, and so on... The type and the configuration of these devices would be different from user to user. CP/M provided a hardware abstraction, so that applications could run on different systems without modifications for a particular hardware.

Thanks,
Sergey
Re: 8085 SBC [message #3099 is a reply to message #3024] Mon, 19 June 2017 16:40 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
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Hi Sergey,
Please excuse me for not responding in a timely manner. I have been suffering from headaches and dizziness all the time now.
Thank you for the interesting information. I kind of assumed there was a standard for I/O for the Altair computer line by the time disk controllers were introduced. My only experience with the Altair was with a multiuser/timeshare type of Basic that ran on an Altair 8800B in College during 1979-81 time frame. 3 Lear Seigler ADM-3A CRT terminals were connected to the Altair 8800B as well as 1 ASR-33 Teletype. There was at least 1 - 8" floppy drive interface and approximately 64KB of RAM. A boot rom was installed that booted the Multiuser Basic from disk. This was my second exposure to programming in the BASIC language. I spent quite a bit of time going through the BASIC Reference Manual on this system.
What I would like to do in addition to whatever else is created for the MiniMaxi8085 board is to be able to run this multiuser basic once again. I still have a Lear Seigler terminal and 2 teletypes that I could eventually hook up to the 8085 once more serial ports were added. Decades ago, I added an RS-232 serial interface to one of my Teletypes so I could run it on my Coco 1 way back in my early 20s.
I really don't know if this software can run unmodified or not. I suspect some mods may be required. It would be so cool to see this software run again from some type memory card.
What type of I/O serial chips were used in the Altair 8800B?
Can the memory card interface on the extension card be made hardware compatible the Disk controller interface of that Altair 8800B Multiuser Basic Setup? I have no idea how much is involved to make this happen or if it is even possible. I guess ideally it would be nice to run all the Altair software, but with all the different I/O setups, I don't know if this is possible either. Please let me know your thoughts. Since the 8085 is binary compatible with the 8080, I thought it would be really cool if the MiniMaxi8085 board could be expanded to become an Altair Clone of sorts.
By the way, what other computers had an 8085 in them?


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc

[Updated on: Mon, 19 June 2017 16:42]

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Re: 8085 SBC [message #3248 is a reply to message #3099] Thu, 20 July 2017 21:08 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
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Hi Guys,
I have finally been able to build my MiniMax8085 board, all except for burning the eprom with MON85 or Tiny BASIC. I'm wondering if the two could be combined into the same eprom with some kind of alteration to MON85 so Tiny Basic could be called from MON85.
I do not know 8085 assembly code at all. I need someone to give me some assistance to achieve this. Any other ideas for software to run on this board would be much appreciated. I'm curious what software other people are using in their boards currently. There's not much one can do with just one serial port. The extension board will be needed to get anything substantial going. What software is currently compatible with this particular platform? Thank you all in advance for any help you guys can give.


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #3251 is a reply to message #3248] Fri, 21 July 2017 11:05 Go to previous messageGo to next message
Sergey is currently offline  Sergey
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I've created an image with MON85 at 0000h, and Tiny BASIC at 1000h. It is attached to this post. Note that the image size is 8 KiB, pad it with 0FFh's for bigger ROM if needed.

Use "G 1000" command from MON85 to start Tiny BASIC. Push the reset button to get back to the monitor.

Moving Tiny BASIC to 1000h required some considerable (but not difficult) modifications. For example the original Tiny BASIC uses RST instructions to call some frequently used subroutines. I had to replace these RST instructions with CALL instructions.
By the way, to me using RST instructions there looks as unnecessary over-optimization... If I am not mistaken using CALL made the binary only about 20 bytes bigger, but still fitting in 2 KiB (assuming that the initial author intention was to fit it in 2 KiB ROM).

[Updated on: Fri, 21 July 2017 11:08]

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Re: 8085 SBC [message #3253 is a reply to message #3251] Fri, 21 July 2017 22:39 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
Senior Member

Hi Sergey,
Thank you so much for responding so quickly AND with a modified program to boot! I'll put it in a 28C256 I have on hand, install it on my MiniMax8085 and let you know how it goes. I really appreciate this very much!
Does anyone have any ideas on how to get some original Altair programs to run on this little marvel of a board? Thanks in advance for any help anyone can give.
Kip


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #3295 is a reply to message #3253] Thu, 03 August 2017 20:43 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 111
Registered: October 2015
Senior Member

Hi Sergey,
I finally finished my 8085 board and it came up the 1st time! Cool! There is only one problem. I can't type anything? I see the power on Message from Mon85 as shown below.

------------------Begin Output--------------------
MON85 Version 1.2

Copyright 1979-2007 Dave Dunfield
2012 Roman Borik
All rights reserved.

C>
------------------ End Output---------------------
That's it. No input.
Here are a couple of pictures of my baord.
index.php?t=getfile&id=557&private=0
index.php?t=getfile&id=558&private=0
I have an 8 channel mini logic analyzer available for troubleshooting.
I used the 15.974MHZ crystal option.
CPU is CA80C85B-8CP.
USART OKI M82C51A-2
Memory AS6C62256 static ram chip.
Eprom is ST M27C256B-10XFI
Lattice GAL16V8D
SN74F573N
Do you have ANY idea why I can see output on power up, but can't type anything? Thanks in advance for any help you can give.
Kip


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc

[Updated on: Fri, 04 August 2017 16:28]

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Re: 8085 SBC [message #3304 is a reply to message #3295] Sat, 05 August 2017 00:33 Go to previous messageGo to previous message
gkaufman is currently offline  gkaufman
Messages: 119
Registered: October 2015
Senior Member
Jumpering looks ok, although picture is difficult to see.
If you have another MAX232A or 82C51 you might try substituting them. and check soldering in that area.
Are you using a terminal program, if so make sure it's not set up to expect hardware or software handshaking.
If all else fails one of the RS232 DB9 inline testers can be helpful.
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