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 Post subject: Re: RB65816-ATX
PostPosted: Tue Sep 29, 2020 8:25 pm 
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ttlworks wrote:
74LS154 seems to be out of production, and it's hard to tell how long 74HCT154 would stay in production.
Would suggest [replacing] the 74154 [with] two 74138's.
GARTHWILSON wrote:
I never understood why the '154 isn't more popular. It seems like it would be as popular as the '138. The last time I looked, there weren't any 154's available in 74AC either.

Dieter, FWIW, according to this Digikey search, TI and Nexperia both list "Active" status for the HCT versions of the '154. And Garth, it seems the AC version is absent, as you suggested.

I like Dieter's solution of using a pair of 138's instead. Also worth considering are the 'HC4514 and 'HC4515 (listed in the search), which are 1-of-16 decoders that feature an input latch you can optionally use. The two chips are identical except the HC4515 has active-high outputs.

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 Post subject: Re: RB65816-ATX
PostPosted: Wed Sep 30, 2020 12:36 am 
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I am curious about the potential for clocking the '816 past 4 MHz in this design. 8 or 12 would be really nice to have as an option.


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 Post subject: Re: RB65816-ATX
PostPosted: Wed Sep 30, 2020 4:50 am 
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commodorejohn wrote:
I am curious about the potential for clocking the '816 past 4 MHz in this design. 8 or 12 would be really nice to have as an option.

8 MHz might be possible with 74HC logic. I have my doubts with 12 MHz.

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 Post subject: Re: RB65816-ATX
PostPosted: Wed Sep 30, 2020 5:25 am 
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GARTHWILSON wrote:
[wider PCB traces to thru-hole connector pins]
We've never had a problem though, so I think the request comes from paranoia.

Long time ago when I did TV repairs for a living, I had seen a lot of PCBs that had failed due to simple mechanical problems.
It had been cheap PCB material, of course... but better safe than sorry.
If one wants to replace a defective ISA connector, maybe damaged by plugging in a self_built card, he usually would wish to have had wider PCB traces.

Dr Jefyll wrote:
Dieter, FWIW, according to this Digikey search, TI and Nexperia both list "Active" status for the HCT versions of the '154.

Jeff, I'm aware that 74HCT154 is listed as active now.
But nobody could tell if it's still active by the time when Ruud starts populating the PCB with components... or when he tries to build another board of that sort in a few years :lol:
//If you do hardware design for a living, >90% of the design might be "dogma and logistics" nowaday.


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 Post subject: Re: RB65816-ATX
PostPosted: Wed Sep 30, 2020 6:19 am 
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ttlworks wrote:
GARTHWILSON wrote:
[wider PCB traces to thru-hole connector pins]
We've never had a problem though, so I think the request comes from paranoia.

Long time ago when I did TV repairs for a living, I had seen a lot of PCBs that had failed due to simple mechanical problems.
It had been cheap PCB material, of course... but better safe than sorry.

I have been impressed at how much PCB-manufacturing technology has improved since the 1990's, not to mention the 1970's. Today even DirtyPCBs seems to give better quality and reliability at nearly free prices than we used to get for thousands of dollars 25 years ago from major PCB manufacturers.

When I worked in repairs at TEAC in the early 1980's, I think the only problems we ever had with actual boards themselves was just that the holes were not thru-plated, and relays would jerk when they were actuated or released and gradually crack the solder around the pins. The copper foil itself was not cracking though, so merely re-flowing the solder with the soldering iron fixed it. Before we figured that out, we replaced a lot of relays that we thought had become intermittent.

In the mid-90's, at the company I'm still at, the two types of board problems we had were always on inner layers of multi-layer boards, and were results of contamination in the PCB-manufacturing process. They seem to have conquered those; so clearly the technology has matured a lot.

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 Post subject: Re: RB65816-ATX
PostPosted: Wed Sep 30, 2020 9:55 am 
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ttlworks wrote:
That VT82C42 heyboard\mouse controller seems to be very exotic.

It still can be bought and it doesn't have to this one; any keyboard controller from an PC ATX board most probably will do. I also have some JetKeys laying around.

Quote:
... PIC18F452 has a parallel slave port, but PIC coding ain't fun.

The VT82C42 and other keyboard controllers are already pre-programmed. I wouldn't mind using a PIC or Atmel if I had sources that go with them. But I didn't even search because I already have the parts.

Quote:
DS12885 real time clock is a bit "outdated", and the bus interface isn't a nice one.

I agree but again, I have them and other types laying around. As mentioned before, the Eagle schematics are free; you don't like, just change it!

Quote:
To me the 29F010 EEPROM looks a bit small.

Bit baffled: uhh, why? IMHO 4 kB should be enough to load what ever OS or software you want to use. If needed, the 6522 can be used to bit-bang a SD card. And even then 4 KB should be enough. My personal idea is to use an HDD card in 8- bit mode with a CF card.

Quote:
Mouser has Microchip SST39SF010A, SST39SF020A, SST39SF040

I have 020s and 040s laying around as well. 128 KB is a nice value. Unless you have a good reason to use a bigger EEPROM; I always can use some of the I/O pins of the 6522 to swap the various 64 KB blocks.

Quote:
multipcb: 2 layers 4WD 121€ (2 layers 13WD 100€), 4 layers 5WD 200€ (4 layers 13WD 166€). //'WD' means 'workdays'.

Have a look at https://jlcpcb.com/. I already used their services.

Quote:
Hmm... if you should be running out of PCB space,

The original ATX is 9.5"x9.5". My board is smaller.

Quote:
BTW: At ca. 30€, Meanwell RQ-125B doesn't seem to be much more expensive than a new ATX power supply at ebay.

Why should I? The ATX board is meant to be placed in a PC case. I regularly receive older PCs to scrap for parts so that leaves me with empty cases and power supplies.

Quote:
FTDI has some chips with USB host functionality.

I always can make an ISA card with USB functionality. That is the nice thing about ISA. Maybe the average won't find many ISA cards on its way but then, why not making some of your own?

Quote:
For Ethernet, take a look at....

To be honest, I'm not that interested in Ethernet. If I become interested, I'll first have a look at the various 3COM cards I have at home. If that doesn't work out, then I will steal Daryl's work :)

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 Post subject: Re: RB65816-ATX
PostPosted: Wed Dec 30, 2020 7:28 pm 
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commodorejohn wrote:
I think for non-trivial cards (NICs, etc.) your best bet would probably be to look at older freenix sources....

This. I worked on the 3Com drivers for NetBSD back in the '90s, and they're not terribly complex. We did everything via direct access, ignoring any ROMs on the board, if they were even present. (The worst part about the drivers were just the tricks to deal with bugs on certain revisions of the boards, but all that is in the freely available source code so you'll at least know what the problems and their solutions are.)

ttlworks wrote:
Using a 4 layer PCB (with GND and +5V at the inner layers)....

Having recently watched the video The Extreme importance of PC Board Stack-up (recently posted by BigEd), I now know that you do not want to separate a signal layer from its ground plane by a +5V plane. :-)

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 Post subject: Re: RB65816-ATX
PostPosted: Fri Jan 01, 2021 3:55 pm 
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If you look at the Micro-PET, I am working on VGA timing, and in SPI interface, included in a single CPLD.

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 Post subject: Re: RB65816-ATX
PostPosted: Sun Jan 03, 2021 10:28 am 
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I like your project. I had started a project using an PC ISA backplane for much the same reason. A couple of things I shoot about. Could you reduce the number of slots? Most modern PCs have fewer than eight slots. I don’t think I ever used all the slots in the PC. Could the bus be faster with fewer slots to drive? After a VGA card, audio card, and disk, what is there (these could also all be on one card these days)? How about providing for some of Garth’s ram modules (or other ram modules) on the motherboard?

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