Topics

1861 Replacement


cmdrcosmac
 

Hi all,

 I'm planning to build Chuck Yakym's 1861 replacement circuit and would like
to hear the Group's experience and advice.
 
 Would using 74HC rather than LS logic work?

 I would like to use a 28C256 EEPROM for the timing ROM as I can program these
on the Elf. There was apparently  some issue with different types of EPROMS in
this circuit. Has this been explained or resolved?

 Has anyone tried to re-do the timing to generate VGA timing rather than NTSC?

Thanks for your help.
-Chuck

 


Rizal Acob
 

Curious...any link where Chuck’s 1861 replacement circuit might be. Thanks


Mark Graybill
 

On Fri, Sep 11, 2020 at 2:56 AM Rizal Acob <racob@...> wrote:
Curious...any link where Chuck’s 1861 replacement circuit might be. Thanks








cmdrcosmac
 

The design I'm building id Chuck Yakym's Rev E, not the STG design.
Since Chuck Yakym's file area on the Group is under construction I've attached
the files. The REV E is the video board, The autorun is an 1802 system made to test the video board
-Chuck


 

  FWIW, all the files for the STG1861 are in the STG Elf2K files area of this group...

Bob


Mark Graybill
 

Sorry I misunderstood. Thanks for the files.


On Fri, Sep 11, 2020 at 11:35 AM cmdrcosmac <cmeyer@...> wrote:
The design I'm building id Chuck Yakym's Rev E, not the STG design.
Since Chuck Yakym's file area on the Group is under construction I've attached
the files. The REV E is the video board, The autorun is an 1802 system made to test the video board
-Chuck


the-eagle@att.net
 
Edited

Chuck, I have attached the Rev. D which is the last one I personally built and tested. I have also included the EPROM - U7 hex file that is needed.

Cheers,
Chuck Yakym


Lee Hart
 

cmdrcosmac wrote:
The design I'm building id Chuck Yakym's Rev E, not the STG design.
Since Chuck Yakym's file area on the Group is under construction I've
attached
the files. The REV E is the video board.
I designed the original using just 4 chips; a 4040, EPROM, and a couple gates. It worked, but the 4040 is a ripple counter, so there were glitches as it advanced to the next state. The EPROM would momentarily look up the wrong address, so there were glitches in the outputs.

Chuck and I worked on improving the circuit. A 74HC4040 is faster, and reduced (but didn't eliminate) the glitches. Chuck used three 74HC163 synchronous counters in his rev.E version; they eliminated the glitches going into the EPROM addresses; but the EPROM itself still has small glitches in its outputs as the addresses change.

I improved it still further in my VIP2K design. I kept the 4040, but added an octal latch on the EPROM outputs, which eliminates the glitches entirely. But the VIP2K board is so tight on space that I couldn't latch all the EPROM outputs (I needed two sections of the octal latch for a /4 counter).

Back to the original question: Yes, this circuit can be configured to do other video formats (other resolutions, separate sync and video, PAL, VGA, etc.) It's basically a state machine, so the clock frequency and EPROM program can be changed for just about any format.

Lee
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com


Peter Renaud
 

Hi,

Is the U7 EPROM code for the Rev D board identical to the Rev B version?
The only difference is the pin 15 HSYNC line which is not connected in Rev D.

Thanks.


From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of the-eagle@... <The-Eagle@...>
Sent: Friday, September 11, 2020 2:52 PM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: Re: [cosmacelf] 1861 Replacement
 

[Edited Message Follows]

Chuck, I have attached the Rev. D which is the last one I personally built and tested. I have also included the EPROM - U7 hex file that is needed.

Cheers,
Chuck Yakym

Virus-free. www.avast.com


the-eagle@att.net
 

Peter, Pin 15 HSYNC isn't used on either design, it was a test output of the EPROM. The U7 EPROM-U7.hex file should work on both the Rev. B and Rev. D. Rev. B was made back in 2011 and the Rev. D was made in 2019.

Cheers,
Chuck Yakym


Peter Renaud
 

Ok, thanks.
I decided to use the Rev B design for my expansion board.
Cheers.


From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of the-eagle@... <The-Eagle@...>
Sent: Monday, September 14, 2020 10:30 AM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: Re: [cosmacelf] 1861 Replacement
 
Peter, Pin 15 HSYNC isn't used on either design, it was a test output of the EPROM. The U7 EPROM-U7.hex file should work on both the Rev. B and Rev. D. Rev. B was made back in 2011 and the Rev. D was made in 2019.

Cheers,
Chuck Yakym

Virus-free. www.avast.com


the-eagle@att.net
 
Edited

Peter, It just came to mind that in my Rev. B and Rev. D replacement circuit I have a minor problem that I have since corrected in my Rev. E which was made 2 weeks (July 20, 2019) after I made the Rev. D. The error in the forming of the SR (Set/Reset) flip-flop U4 and U5 to make, these are non-matching gates, the results are that the DIS ON will turn the circuit on however the DIS OFF will NOT turn the circuit off. I have now made the DIS ON, DIS OFF, SR flip-flop out of 2 gates in U4. Please see the attached Rev. E schematic to see the change I made on the DIS ON and DIS OFF lines.

Chuck


Peter Renaud
 

Hi,

Thanks for the heads up.
I have the SR in U4 as I had to revise that circuit because of my Nx lines being active low.
I have attached my current draft design schematic and PCB for your review.
I am in the process of revising it before sending to the JLCPCB fab.
The expansion board is a prototype that connects to my SBC 1802 V3 card.
It provides the CDP1861 Rev B circuit, a PS/2 interface (make characters only) and a I/O port which replaces the one on the V3.

Cheers.


From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of the-eagle@... <The-Eagle@...>
Sent: Monday, September 14, 2020 12:58 PM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: Re: [cosmacelf] 1861 Replacement
 
Peter, It just came to mind that in my Rev. B and Rev. D replacement circuit I have a minor problem that I have since corrected in my Rev. E which was made 2 weeks (July 20, 2019) after I made the Rev. D. The error in the forming of the SR (Set/Reset) flip-flop U4 and U5 to make, these are non-matching gates, the results are that the DIS ON will turn the circuit in however the DIS OFF will NOT turn the circuit off. I have now made the DIS ON, DIS OFF, SR flip-flop out of 2 gates in U4. Please see the attached Rev. E schematic to see the change I made on the DIS ON and DIS OFF lines.

Chuck

Virus-free. www.avast.com


Randy Eubanks
 

Chuck,

Are bare boards available for your 1861 replacement circuit? If not, are Gerber or alternate format files available such that I could have a few made?

Thanks, Randy


the-eagle@att.net
 


Randy,

I don't have any PCB's or Gerber files. Soon I plan on doing a PCB layout of the Rev. E board.

Chuck


the-eagle@att.net
 

Randy,

I don't have any bare boards laying around. Soon I plan on having a few made.

Chuck


P Todd Decker
 

Count me in for a Rev E board

---
P. Todd Decker
913-284-8814

On Sep 14, 2020, at 2:03 PM, the-eagle@... <The-Eagle@...> wrote:


Randy,

I don't have any PCB's or Gerber files. Soon I plan on doing a PCB layout of the Rev. E board.

Chuck


 

Sounds great.  I'll be looking forward to that.  It would be fun to build at least one.

Dave


P Todd Decker
 

FYI -- There is an RCA COSMAC 1861 being offered on eBay from a domestic seller for $70 plus $4.80 shipping:  https://www.ebay.com/itm/184448193087?ul_noapp=true


gregory simmons
 

Also, a very pretty white and gold Harris 1802 from the same seller, same price.
========================================

On Tuesday, September 15, 2020, 10:31:22 AM EDT, P Todd Decker via groups.io <ptdecker@...> wrote:


FYI -- There is an RCA COSMAC 1861 being offered on eBay from a domestic seller for $70 plus $4.80 shipping:  https://www.ebay.com/itm/184448193087?ul_noapp=true