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Re: 8085 SBC [message #3305 is a reply to message #3295] Sat, 05 August 2017 04:18 Go to previous messageGo to next message
christiankeck is currently offline  christiankeck
Messages: 5
Registered: October 2015
Junior Member
The OKI M82C51A-2 receive state machine might not operate at clock rates of 7,5 MHz. The M82C51A-2 is specified for 5 MHz only.

Christian
Re: 8085 SBC [message #3310 is a reply to message #3305] Sat, 05 August 2017 13:00 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 130
Registered: October 2015
Senior Member

Hi Christian,
Well that makes since. I didn't know the chip I chose was 5MHZ only. Had I known, I would have sought after a different speed chip.
I know someone is or has clocked their 8085 at 15.9MHZ or 16MHZ so I'm wondering what chip they used as their 82C51? An inquiring mind wants to know! Smile


Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
Re: 8085 SBC [message #3312 is a reply to message #3310] Sat, 05 August 2017 15:06 Go to previous messageGo to next message
christiankeck is currently offline  christiankeck
Messages: 5
Registered: October 2015
Junior Member
The OKI 1998 datasheet for the MSM82C51A-2 states a CLK input minimum cycle time of 160 ns or 180 ns, which corresponds to 6,25 MHz and 5,56 MHz respectively. I cite: "CLK signal is used to generate internal device timing. CLK signal is independent of RXC or TXC.
However, the frequency of CLK must be greater than 30 times the RXC and TXC at ... Asynchronous "x1" mode, and must be greater than 5 times at Asynchronous "x16" and "x64" mode." You might try to generate the CLK signal by dividing the CPU's CLK OUT signal by 2 using the GAL.

Christian
Re: 8085 SBC [message #3318 is a reply to message #3312] Sun, 06 August 2017 11:29 Go to previous messageGo to next message
davetypeguy is currently offline  davetypeguy
Messages: 41
Registered: November 2015
Location: Chapin, SC
Member
Hi Kip,

On my 5MHz board I used the OKI M8251A-2 and on my working 8MHz board I am using a Toshiba TMP8251AP. Having said that, I don't believe I purposefully chose that chip. In fact, looking at the datasheets, it would appear the Toshiba 8251AP-8 is the 8MHz rated part and this chip (the TMP8251AP) is only rated for 3.125MHz (Tcyc min is 320ns). Having said all that, it appears to work fine. I can swap the chips later tonight to see if the OKI chips I have works at 8MHz. I believe that is the chip that Sergey's board used at 8MHz and it worked fine. It could be your chip, or maybe a problem with the cable or MAX232? Does it work correctly at 5MHz?

Dave
Re: 8085 SBC [message #3336 is a reply to message #3318] Mon, 07 August 2017 14:12 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 236
Registered: October 2015
Location: Portland, OR
Senior Member
Hi Kip,

I apologize for delayed reply. I second Gary's suggestion to double-check the handshaking/flow control settings in your terminal emulation software - make sure you have RTS/CTS flow control enabled. Otherwise you won't not able to send anything to your 8085 board, since 8251 will be waiting for the CTS signal (on 8085 board side) to become active before receiving the data.
As a quick test you might try disconnecting RTS (pin 7) and CTS (pin 8) on DE9 connector of the 8085 board from your terminal/PC, and connecting them together (kind of a RTS/CTS loopback).

While Christian is right regarding CLK frequency specifications (160 ns minimal period = 6.25 MHz), in my case 82C51A-2 works perfectly fine with 8 MHz CLK.

Best regards,
Sergey

[Updated on: Mon, 07 August 2017 14:12]

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Re: 8085 SBC [message #3338 is a reply to message #3336] Tue, 08 August 2017 18:48 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 236
Registered: October 2015
Location: Portland, OR
Senior Member
Actually, I rechecked my setup on the 8 MHz system, and I have Toshiba TMP82C51AP-10, which is rated for 10 MHz clock...
Re: 8085 SBC [message #3339 is a reply to message #3338] Tue, 08 August 2017 19:27 Go to previous messageGo to next message
computerdoc is currently offline  computerdoc
Messages: 130
Registered: October 2015
Senior Member

Hi Sergey,
Thank you so much for checking the chip you used on your 8MHZ board. That will definitely be the one I will get then. I just found some on ebay and got them. Thanks for the information Sergey.


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

[Updated on: Tue, 08 August 2017 20:21]

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Re: 8085 SBC [message #3343 is a reply to message #3339] Wed, 09 August 2017 06:42 Go to previous messageGo to next message
gkaufman is currently offline  gkaufman
Messages: 186
Registered: October 2015
Senior Member
The only TMP82C51AP-10's on Ebay currently are from UTSource/China and appear to be "refurbished" parts.

If that's where you ordered I'd seriously doubt that they are really 10mhz rated parts. They look like they have been topcoated and re-silk screened.

Why not drop back to 3.072mhz for testing?

- Gary

computerdoc wrote on Tue, 08 August 2017 19:27
Hi Sergey,
Thank you so much for checking the chip you used on your 8MHZ board. That will definitely be the one I will get then. I just found some on ebay and got them. Thanks for the information Sergey.

Re: 8085 SBC [message #4771 is a reply to message #2280] Sat, 23 June 2018 03:08 Go to previous messageGo to next message
christiankeck is currently offline  christiankeck
Messages: 5
Registered: October 2015
Junior Member
Hi, all,

someone from Germany is trying to sell a Minimax8085 on ebay. He does not mention that it orginates from Sergey's Minimax8085 project and has set a starting price, which is considerably higher than the cost of materials:
https://www.ebay.de/itm/8085-Einplatinencomputer/17337599783 3?hash=item285e03c789:g:FFcAAOSw4eJbIO3g or search for 8085 Einplatinencomputer.

Christian
Re: 8085 SBC [message #4777 is a reply to message #4771] Sun, 24 June 2018 01:07 Go to previous messageGo to next message
b1ackmai1er is currently offline  b1ackmai1er
Messages: 396
Registered: November 2017
Senior Member
Expensive but being sold as second hand, seller selling a range of stuff so not a business selling homebrew as a commercial venture. I don't see anything wrong with this.

Better to pass it on to someone who will use rather than sit on a shelf.

Would be interested in hearing retrobrew creators opinions.

Good reminder for me to start building mine while I wait for my ECB board parts to arrive from China - I didn't know about or remember this thread Smile

Regards Phil.

[Updated on: Sun, 24 June 2018 01:11]

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Re: 8085 SBC [message #4778 is a reply to message #4777] Sun, 24 June 2018 09:41 Go to previous messageGo to next message
Andrew B is currently offline  Andrew B
Messages: 467
Registered: October 2015
Location: Near Redmond, WA
Senior Member
Administrator
eBay recently changed their policy on links and won't allow any links in descriptions anymore. Which makes it hard to properly attribute things like this. The seller does say "Documents can be provided as a link to the website (Google: MiniMax8085)"

It is Sergey's design, not mine - but I would say unless someone is creating a commercial venture, most people here wouldn't mind. Also Sergey put an open source hardware logo on the bottom silkscreen Smile
Re: 8085 SBC [message #4789 is a reply to message #4778] Mon, 25 June 2018 15:56 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 236
Registered: October 2015
Location: Portland, OR
Senior Member
Hi,

The MiniMax8085 is an open source project (and so are most of my other projects). Anyone is allowed to manufacture these designs, and sell them, be that for profit, or otherwise.

It would be nice though, if whoever is planning to mass-produce and sell PCBs, kits, or assembled boards, will contact the project author(s) and notify them. At least it would give us an opportunity to share the experience and suggestions about the project, get some idea about the interest or demand for that project, and clarify the support structure.

And by the way, a few people had approached me about selling the PCBs, or even making and selling the kits. Also, I know about several people who had manufactured and distributed some of my designs (without notifying me first). Either way, it is OK.

In this particular case, as people commented above, it doesn't look that the seller is mass-producing these boards, and likely tries to sell his own board. While the price might be higher than the price of the components, I don't see anything wrong with that. It is really up to the eBay seller to set the price.

Thanks,
Sergey
Re: 8085 SBC [message #5189 is a reply to message #4789] Mon, 17 September 2018 04:01 Go to previous messageGo to next message
rvumbaca is currently offline  rvumbaca
Messages: 17
Registered: September 2018
Junior Member
Hi,

Bit of a long shot - but does anyone know where I might be able to source a working Tundra/Calmos 80C85A-8 (8 MHz)? Or does anyone want to sell me one?

I tried to buy one on EBay but it was defective. I then bought two from UTSource but one was defective and the other proceeded to self-combust.

All three of these defective parts had identical markings so I'm thinking that there's a big batch of useless/countefeit/reject 80C85A-8 chips currently coming out of some dodgy factory in China. I don't know why they bother, all of the sellers had to refund me my money anyway.

Apart from that I built a Minimax8085 and it works great with an Oki 80C85 CPU (5 MHz)! Thanks for the design Sergey.

Thanks,
Rosario
Re: 8085 SBC [message #5190 is a reply to message #5189] Mon, 17 September 2018 10:23 Go to previous messageGo to next message
Sergey is currently offline  Sergey
Messages: 236
Registered: October 2015
Location: Portland, OR
Senior Member
Hi Rosario,

Unfortunately Chinese and Hong Kong based sellers frequently sell refurbished or relabeled parts. I personally prefer to buy locally (e.g. US sellers), or at least sellers that offer free returns/exchange.

Here are a few things I'd pay attention to when ordering ICs of the eBay:
- How the seller describes the part? "New" on a 1990's part sounds suspicious. It is possible that that some might have NOS (new old stock) parts, but they are not that common. Used/refurbished might sound more reasonable and honest. Although, I doubt a seller would have capability to test the ICs.
- Check the date code - usually a four digit number in YYWW - year/work week format. Is it too new for the part? It would be surprising to see 80C85 a part made in 2000's. Or maybe it is completely wrong, for example the work week value is above 52.
- Pay attention to the labeling. Yellowish-gray laser etched marking was not used in 1980's-1990's. If you see an older part with such marking, most likely it was relabeled.
- Parts have the same labeling, but the packages a bit differ (slightly different shape, pin 1 indent is different, the marking on the bottom are different or missing). All this is a sign of relabeling.
- Pins have signs of desoldering. They are shiny, not uniform. (New IC would have more of a flat, grayish finish).

Now, with this hobby, it is quite possible that buying ICs from China is the only choice. But at least eBay sellers are usually pretty good about returns and refunds...

BTW, maybe give this one a try: https://www.radwell.com/en-US/Buy/GENERIC/GENERIC/CA80C85B8C P

Hope this helps,
Sergey

[Updated on: Mon, 17 September 2018 15:16]

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Re: 8085 SBC [message #5191 is a reply to message #5190] Mon, 17 September 2018 11:08 Go to previous messageGo to next message
Andrew B is currently offline  Andrew B
Messages: 467
Registered: October 2015
Location: Near Redmond, WA
Senior Member
Administrator
From looking at a Tundra document - http://bitsavers.trailing-edge.com/components/tundra/9000000 .MD302.01_Tundra_8000_Series_Components_Manual_1996.pdf - it looks like CA80C85B-8CP may be what you want, and was made until at least 1996.

The 5MHz OKI version might run at 8MHz as well, if you can't find the 8 MHz version.
Re: 8085 SBC [message #5193 is a reply to message #5190] Mon, 17 September 2018 15:50 Go to previous messageGo to next message
rvumbaca is currently offline  rvumbaca
Messages: 17
Registered: September 2018
Junior Member
Hi Sergey,

Thanks for you response. I'm know the risks well, but I have no choice as I am based in Australia. There are no local sellers. Fortunately it is easy to get my my money back when using PayPal.

The worst thing with China sellers is that the photo rarely matches what you receive. Although the photo at UTSource looked like the real part, the received part was not real at all.

I did identify Radwell/PLCCenter as a source, but they charge $150+ for shipping to Australia which is a joke. They also have a poor reputation from their EBay feedback.

Therefore if anyone on this forum would like to sell me a spare and working Tundra CA80C85B-8CP, I would be very happy to buy it from you. I'm not looking for a new part, I just want a part that works (unlike the garbage I received from China).

Regards,
Rosario
Re: 8085 SBC [message #5194 is a reply to message #5193] Mon, 17 September 2018 16:05 Go to previous message
rvumbaca is currently offline  rvumbaca
Messages: 17
Registered: September 2018
Junior Member
Hi Andrew,

I suppose I could try to overclock the Oki chip Smile
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