Date   

Re: Noob question: examine arbitrary memory address? #memory #ELF

Lee Hart
 

How does the RC1802 drive the TIL311 hex displays?
David Schultz wrote:
MC14495 latch and hex to seven segment decoder
Ah! No CMOS loading problems there.

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


COSMAC in Japan

John Kennedy
 

フライヤーが届きました。#MFTokyo2020 #COSMAC研究会 https://twitter.com/kanpapa/status/1309810302234501120/photo/1

Something interesting happening.. wish I knew what!


Re: Noob question: examine arbitrary memory address? #memory #ELF

joshbensadon
 

If changed to HC, then the 47K will work just fine.



From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of P Todd Decker via groups.io <ptdecker@...>
Sent: Saturday, September 26, 2020 3:10 PM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: Re: [cosmacelf] Noob question: examine arbitrary memory address? #ELF #Memory
 
Should all the LS chips be replaced with HC?  And, if so, can the originally specified 47K resistor values be maintained?

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

On Sep 26, 2020, at 1:24 PM, Lee Hart <leeahart@...> wrote:

ca1naj610 wrote:
> Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10.
> Since many of us have 74HC chips, what would be the consequence of
> substituting a 74HC10 for the 74LS10?

Sure; a 74HC10 would work as well as the 74C10. I was just thinking of a vintage chip that would have been Elf-period correct, without having to rewire it for a 4023.

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











Re: Noob question: examine arbitrary memory address? #memory #ELF

David Schultz
 

On 9/26/20 2:51 PM, Lee Hart wrote:

That makes me wonder: How does the RC1802 drive the TIL311 hex displays?
The PE Elf used eight 4050 buffers to drive its display, because these
are TTL parts. They would overload the bus without the buffers.
MC14495 latch and hex to seven segment decoder

--
http://davesrocketworks.com
David Schultz


Re: Noob question: examine arbitrary memory address? #memory #ELF

John Kennedy
 

It doesn’t use TILs, it uses a common cathode 7-segment LED display.


Re: Noob question: examine arbitrary memory address? #memory #ELF

Lee Hart
 

P Todd Decker via groups.io wrote:
Should all the LS chips be replaced with HC? And, if so, can the originally specified 47K resistor values be maintained?

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

On Sep 26, 2020, at 1:24 PM, Lee Hart <leeahart@...> wrote:

ca1naj610 wrote:
Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10.
Since many of us have 74HC chips, what would be the consequence of
substituting a 74HC10 for the 74LS10?
Sure; a 74HC10 would work as well as the 74C10. I was just thinking of a vintage chip that would have been Elf-period correct, without having to rewire it for a 4023.
I haven't looked at the RC1802 schematic closely. But the diode OR gates in the original PE Elf used 47k pull-down resistors. Since they all drove CMOS inputs, it worked.

The problem comes because the N2/LOAD signal can't drive a 74LS input (much less 3 of them, as would happen if the PE Elf's IC10 was a 74LS10 instead of a 4023).

That makes me wonder: How does the RC1802 drive the TIL311 hex displays? The PE Elf used eight 4050 buffers to drive its display, because these are TTL parts. They would overload the bus without the buffers.

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


Re: Noob question: examine arbitrary memory address? #memory #ELF

P Todd Decker
 

Should all the LS chips be replaced with HC? And, if so, can the originally specified 47K resistor values be maintained?

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

On Sep 26, 2020, at 1:24 PM, Lee Hart <leeahart@...> wrote:

ca1naj610 wrote:
Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10.
Since many of us have 74HC chips, what would be the consequence of
substituting a 74HC10 for the 74LS10?
Sure; a 74HC10 would work as well as the 74C10. I was just thinking of a vintage chip that would have been Elf-period correct, without having to rewire it for a 4023.

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


Re: Noob question: examine arbitrary memory address? #memory #ELF

Lee Hart
 

ca1naj610 wrote:
Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10.
Since many of us have 74HC chips, what would be the consequence of
substituting a 74HC10 for the 74LS10?
Sure; a 74HC10 would work as well as the 74C10. I was just thinking of a vintage chip that would have been Elf-period correct, without having to rewire it for a 4023.

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


Re: Noob question: examine arbitrary memory address? #memory #ELF

John Kennedy
 

In my case the wrong chip was stopping the strobe signal from being pulled low, so the display was not useful. Gates on the same chip also drove the TX/RX pins and so those didn’t work properly either.


Re: Noob question: examine arbitrary memory address? #memory #ELF

ca1naj610
 

Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10.  Since many of us have 74HC chips, what would be the consequence of substituting a 74HC10 for the 74LS10? 

Denny Ruigenstein


Re: COSMAC ELF Video Board

Mark Clegg
 

Back in the late 70's....

After my Elf II,  I had a homebrew 1806 system which used the TMS9929A (PAL version of the 9918) for it's video output, it worked fine, and is relatively easy to interface as I remember. You can use either a couple of I/O ports, or just one and the Q line.

My current homebrew system, which some of you may have seen on the Cosmac Elf 1802 Facebook group doesn't have video out yet, but the plans are to add a video board using that very same chip (assuming it still works).

Mark.

On 26/09/2020 13:44, Alan Jones wrote:
Folks,
I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?

Al, N8WQ


Re: Noob question: examine arbitrary memory address? #memory #ELF

Lee Hart
 

Tor-Eirik Lunde wrote:
Yeah... I'm a bit of an amateur when it comes to electronics, so when it
comes to faults I can just about figure out the logic of things.

Nice going on finding a fix for the errors in my ways. Will have to
revisit the design once I get a semblance of a hobby workshop up and
running again 😀
No worries, mate. Hobbies are all about fun and new experiences. We learn more from our mistakes than from our successes. :-)

On the 74LS10: One way to avoid fix it is to use a 74C10. It's CMOS, and is a plug-in replacement for the 74LS10 (same pinouts). But it's an old chip and a bit hard to find.

Lee Hart

--
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


Re: Noob question: examine arbitrary memory address? #memory #ELF

John Kennedy
 

Tor-Eirik - thanks for sharing your design! I had a lot of fun and learnt a lot by building it!


ELF Memory? HM-6551-5, 256x4, DIP-22, 0.4" wide

 

Can you Gentlemen confirm that this old Harris CMOS RAM chip circa' 1979 will work correctly as a substitute for the '2101 chips in the original PE ELF circuit, please?

TIA.  Cheerful regards, Mike, K8LH




Re: COSMAC ELF Video Board

Stephen Cass
 

At IEEE Spectrum, we ran a pair of articles by one of the people involved in the creation of the 9900 processor used in the TI 99/4A, and how the weird memory architecture arose that you might find interesting: here's the second article that focuses on the computer:


Cheers,

S.



On Sat, Sep 26, 2020 at 9:08 AM <wrcooke@...> wrote:
There should be no reason you couldn't use that on an 1802.  But it may not be as simple as it first appears.  The 9918 is designed to use a separate memory space, directly accessible only to itself.  In addition, that memory interface is designed for 16K dynamic RAM chips.  So, you will need to somehow provide that memory either with compatible chips or some additional circuitry to interface to more modern chips.  All 9918 access to itself or to the video memory is (IIRC) through a couple of I/O ports.  That "should" be relatively straightforward to connect to the 1802.

The 9918 datasheet is available here:

Will

On 09/26/2020 7:44 AM Alan Jones <oalanjones@...> wrote:


Folks,
I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?

Al, N8WQ


Re: Noob question: examine arbitrary memory address? #memory #ELF

joshbensadon
 

Hi Tor-Eirik,

I guess it's your design.  There's no better way of testing a project than by having a group build!  When you finish the corrections on the design, would you consider doing a board run for the group?

Cheers,
Josh Bensadon
Toronto



From: cosmacelf@groups.io <cosmacelf@groups.io> on behalf of Tor-Eirik Lunde <teblunde@...>
Sent: Saturday, September 26, 2020 7:57 AM
To: cosmacelf@groups.io <cosmacelf@groups.io>
Subject: Re: [cosmacelf] Noob question: examine arbitrary memory address? #ELF #Memory
 
Yeah... I'm a bit of an amateur when it comes to electronics, so when it comes to faults I can just about figure out the logic of things. 

Nice going on finding a fix for the errors in my ways. Will have to revisit the design once I get a semblance of a hobby workshop up and running again 😀

lør. 26. sep. 2020, 04:18 skrev David Schultz <david.schultz@...>:
On 9/25/20 8:46 PM, John Kennedy wrote:
>
> I unsoldered and replaced D6, D7 and the 74LS10.
> Interestingly the LOW signal at pin 10 of the 74LS10 is exactly as
> expected. However, when the chip is inserted, the logic probe won’t give
> a high or low - there’s a small voltage there. Where could it be coming
> from?

The 47K resistor in the wired-OR is great for CMOS logic but TTL, even
LS TTL, draws more current. A quick check of a data sheet shows input
current  when Vin=0.4V of -0.4mA. Which will create quite the voltage
drop on a 47K resistor.

You could lower that resistance but I can't help but be horrified by the
use of LS TTL with an 1802. 74HC or HCT if you must but please not LS.


--
http://davesrocketworks.com
David Schultz






Re: COSMAC ELF Video Board

wrcooke@...
 

Adding to my previous reply, Steve Ciarcia did a project in Byte with this chip.  You can see there what is required.

Will

On 09/26/2020 7:44 AM Alan Jones <oalanjones@...> wrote:


Folks,
I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?
https://hackaday.com/2020/09/11/tv-output-from-arduino-1980s-style/#more-431395

Al, N8WQ



"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

"The names of global variables should start with    // "  -- https://isocpp.org



Re: COSMAC ELF Video Board

wrcooke@...
 

There should be no reason you couldn't use that on an 1802.  But it may not be as simple as it first appears.  The 9918 is designed to use a separate memory space, directly accessible only to itself.  In addition, that memory interface is designed for 16K dynamic RAM chips.  So, you will need to somehow provide that memory either with compatible chips or some additional circuitry to interface to more modern chips.  All 9918 access to itself or to the video memory is (IIRC) through a couple of I/O ports.  That "should" be relatively straightforward to connect to the 1802.

The 9918 datasheet is available here:

Will

On 09/26/2020 7:44 AM Alan Jones <oalanjones@...> wrote:


Folks,
I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?
https://hackaday.com/2020/09/11/tv-output-from-arduino-1980s-style/#more-431395

Al, N8WQ

_._,_._,_

"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

"The names of global variables should start with    // "  -- https://isocpp.org



Re: Noob question: examine arbitrary memory address? #memory #ELF

P Todd Decker
 

Tor-Eirik—Thank you for contributing your design! I am glad we now know which member did these designs.  It wasn’t obvious to me from your GitHub site. There are five of us now who have your boards and will be building it. And, I know of a sixth who is also interested. You may have also seen from other posts that I have created a more detailed BOM.  Could you take a moment to review it?  Especially the specs for the 7-segment LEDs.  

All — For the rest of us who are preparing to build this, should we switch the resistor value to 3.3K as John did?  Or, should we keep the same resistor and instead change from the 74LS10 to the 4023 or 74HC10?  Are there any other ICs or resistors that we should also change?

On Sep 26, 2020, at 6:57 AM, Tor-Eirik Lunde <teblunde@...> wrote:

Yeah... I'm a bit of an amateur when it comes to electronics, so when it comes to faults I can just about figure out the logic of things. 

Nice going on finding a fix for the errors in my ways. Will have to revisit the design once I get a semblance of a hobby workshop up and running again 😀

lør. 26. sep. 2020, 04:18 skrev David Schultz <david.schultz@...>:
On 9/25/20 8:46 PM, John Kennedy wrote:
> 
> I unsoldered and replaced D6, D7 and the 74LS10.
> Interestingly the LOW signal at pin 10 of the 74LS10 is exactly as
> expected. However, when the chip is inserted, the logic probe won’t give
> a high or low - there’s a small voltage there. Where could it be coming
> from?

The 47K resistor in the wired-OR is great for CMOS logic but TTL, even
LS TTL, draws more current. A quick check of a data sheet shows input
current  when Vin=0.4V of -0.4mA. Which will create quite the voltage
drop on a 47K resistor.

You could lower that resistance but I can't help but be horrified by the
use of LS TTL with an 1802. 74HC or HCT if you must but please not LS.


-- 
http://davesrocketworks.com
David Schultz







COSMAC ELF Video Board

Alan Jones
 

Folks,
I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?
https://hackaday.com/2020/09/11/tv-output-from-arduino-1980s-style/#more-431395

Al, N8WQ