Piggyback 9938?

[+FarmerPotato]

With 9958s being more abundant than 9938s, I was wondering how to make a plug-in replacement. 
 

There would have to be a PCB with a socketed 9958. But those pins are 0.07” spaced (1.778 mm), not the common 0.1” (2.54 mm). How to make the PCB plug in to the old socket?
 

I’m at a loss as to what kind of hardware bits exist that could plug into the original socket. I doubt there is a breakaway header strip of 0.07” spacing. 
EDIT: Yes there is

 

Any ideas?

 

 

[RickyDean]

Are you talking about replacing the 9938 on the Geneve? If so there is already documentation out there and I believe here on atari age to place a 58 in the 38 socket. I believe you need to bend out a few pins and maybe a wire or two. Haven't tried it yet. You lose the myarc mouse support though, I believe.

Edited April 29, 2021 by RickyDean
add sentence.

[wierd_w]

The obvious answer is a socket on a silkscreened PCB, with legs to the side, similar to a breakout board.

 

Use a doublesided PCB, so that one side of the IC's lines are on top, and the other side's are on the bottom, to make routing easier.

 

If vertical height is not a source of concern, use a traditional breakout to IDC single pin strip headers on either side, with two PCBs, connected by the header strips, sandwiched on top of each other.

 

Top PCB has the breakcou to IDC, Bottom PCB has the IDC to socket pin breakout. You could use single-sided PCBs then.

[+Ksarul]

1 hour ago, wierd_w said:

The obvious answer is a socket on a silkscreened PCB, with legs to the side, similar to a breakout board.

 

Use a doublesided PCB, so that one side of the IC's lines are on top, and the other side's are on the bottom, to make routing easier.

 

If vertical height is not a source of concern, use a traditional breakout to IDC single pin strip headers on either side, with two PCBs, connected by the header strips, sandwiched on top of each other.

 

Top PCB has the breakcou to IDC, Bottom PCB has the IDC to socket pin breakout. You could use single-sided PCBs then.

That works fine if the socket you are plugging into has .100 pin separation, as that is the spacing for normal pin headers. That won't work here, as the existing socket is a shrink-DIP socket with .078 pin spacing. The problem is to get single row headers in that spacing. . .it looks like it needs to be 1.98mm. I have seen some headers with 2mm spacing, so it may be possible if the socket tolerances are sufficiently squishy to use them. Here is a header of the right type and with 2mm spacing. It might work, @FarmerPotato. Here is another seller with a slightly better price.

[RickyDean]

Not understanding the question, I was under the impression that he was talking about replacing the 9938 with a 9958, by stacking the new on the old. But the are plenty of sockets which can be cut apart to make sips, just by doing a search for 64 pin sdip sockets on google. But the sdips work fine without being cut too.

[+FarmerPotato]

10 hours ago, RickyDean said:

Are you talking about replacing the 9938 on the Geneve? If so there is already documentation out there and I believe here on atari age to place a 58 in the 38 socket. I believe you need to bend out a few pins and maybe a wire or two. Haven't tried it yet. You lose the myarc mouse support though, I believe.

Yeah, that's one approach. I wondered if there were instructions from someone who has tested it, because that would be good to compare.

 

But I'm really thinking of a PCB so I can add some stuff. Also I'm working on the Geneve2020 video card a lot this week (9958 plus stuff), and I have some thoughts about porting it to the 9640 (or any other 9938 socket.)

[+FarmerPotato]

2 hours ago, Ksarul said:

That works fine if the socket you are plugging into has .100 pin separation, as that is the spacing for normal pin headers. That won't work here, as the existing socket is a shrink-DIP socket with .078 pin spacing. The problem is to get single row headers in that spacing. . .it looks like it needs to be 1.98mm. I have seen some headers with 2mm spacing, so it may be possible if the socket tolerances are sufficiently squishy to use them. Here is a header of the right type and with 2mm spacing. It might work, @FarmerPotato. Here is another seller with a slightly better price.

Sorry, I messed up the numbers on my first post. From memory, typed on my phone, you know. 

 

The pin spacing (pitch) is 1.778 mm, or 0.07 in.

The pin width tapers from 1 mm to 0.48 mm. (0.5 mm square is a common pin size.)

There are 32 pins to a side (the rest is just theory)

 

I was looking at the 2mm headers, to see if they were in tolerance, when I realized it was too good to be true.

32 x 1.778 mm = 56.896 mm, compared to 32 * 2 mm = 64 mm.

 

 

Thanks anyway!

 

[+FarmerPotato]

2 hours ago, Ksarul said:

I have seen some headers with 2mm spacing, so it may be possible if the socket tolerances are sufficiently squishy to use them. Here is a header of the right type and with 2mm spacing. It might work, @FarmerPotato. Here is another seller with a slightly better price.

 

Running with that, I pondered 1.27mm strips. A ridiculous approach would be to cut them up into single pins and put those individually into the board. Yuck. Just putting a 64-pin socket into a PCB is hard enough! Also inserting the 9958.

 

If it came down to attaching machined pins one at a time, like the F18A, I would favor minimizing the number of pins by putting as much as possible on the PCB.

 

For instance, duplicate the VRAM and skip 22 pins. Skip the colorbus because it no longer carries mouse. (Or, hmm, emulate it from a PS/2 mouse.. dang that's a good idea.)

 

So that would leave pins VCC, GND, CD0-7, RESET, VDPINT, MODE1, MODE2, CSW, CSR (16 pins), with the outputs R,G,B,CSYNC. Most of these are at one end of the chip.

 

Still, leaving some pins unattached and floating could be a disaster.

 

Supposing I did manage to DEBUG and port the Geneve2020 video card, the result would be a 9938 plug-in replacement that offers 2 significant features. One, mouse interface from a PS/2 mouse (natch, I just thought of that). Two, VGA upscaler. Three, umm, no shortage of ideas here.

 

Built-in VGA upscaler means no more need for 15kHz RGB monitors. Just a standard, VGA 640x480x60 fps, 25.2 MHz dot clock, compatible with anything. The scheme is to box a 512x424 area inside 640x480. So, pixel doubling as needed to support 256x192, 512x192, or interlaced 256x424 (interlaced is going to suck.) What I'm working on in my spare time this week. Only very basic results so far, but it gives me joy that the VGA out synced perfectly on the first try.

 

 

[RickyDean]

Sounds like your on to a very good start on an amazing idea.

[+Ksarul]

Here are some 1.778mm round pin male header strips for you. . .and another one with a minimum buy of 1,000 parts. Here's another one on eBay. There are plenty of these listed on eBay, from multiple sellers.

[+FarmerPotato]

Aha, they do exist. Shrink-DIP headers and sockets are made by Mill-Max, but they are stupid expensive.

https://www.mouser.com/Connectors/Headers-Wire-Housings/_/N-ay0lo?P=1z0wuwr

https://www.mouser.com/datasheet/2/273/127-259680.pdf

 

The Series 862 is a 21-pin SIP in Pb/Sn. Costs $5.88 or $0.28/pin.

 

While there, I saw a ZIF socket for the 64 pin shrink dip. Neat.  https://www.mouser.com/ProductDetail/3M-Electronic-Solutions-Division/264-1300-00-0602J?qs=RC2ne4458IJ4jJEk8ff9ng%3D%3D

 

[+FarmerPotato]

8 minutes ago, Ksarul said:

Here are some 1.778mm round pin male header strips for you. . .and another one with a minimum buy of 1,000 parts. Here's another one on eBay. There are plenty of these listed on eBay, from multiple sellers.

Thanks! You are the best electronics shopping buddy.

[+dhe]

So... For those of us that are a little slow.

 

1) Why would you want to piggy back a chip instead of just pull and replace? (Especially since it IS in a socket)?

2) Is the socket itself unobtainable?

[RickyDean]

The socket's definitely are not unobtainium. Just do a search for 64 pin sdip sockets. Plenty of them. Think @FarmerPotatoe was thinking of just piggy backing on a dead 9938 on a Geneve that did not have a socket (some do exist, I believe). But to me that wouldn't be the way to handle it. Machined, or dual wipe sockets all the way, buddy...?

Edited April 30, 2021 by RickyDean
spelling

[+Ksarul]

4 hours ago, dhe said:

So... For those of us that are a little slow.

 

1) Why would you want to piggy back a chip instead of just pull and replace? (Especially since it IS in a socket)?

2) Is the socket itself unobtainable?

There are a few differences between the 9938 curently in the socket and the 9958 we want to replace it with. Using a piggy-back socket allows us to make those pin changes in an elegant fashion. I did a similar thing when I wanted to make a 27C4000/27C4001 adapter for my EPROM programmer. On the sockets used for the 9938/9958, I think I have about 1,000 of them. . .so they are available to us.

[+9640News]

It's been a very long time, but back in the 90's, I tried to substitute a 9958 for the 9938 on the Geneve.  I don't recall specifically what I may have done with some of the incompatible pinouts, but as I recall, the 9958 plugged into the 9938 socket on the Geneve.  As I recall, I had some circuitry to handle the separate R, G, and B lines to go to some video output.  Not sure if it was VGA, or something else.  

 

 

[+FarmerPotato]

Yeah, piggyback implies a chip on top of another chip. Like doubling the SRAM. 

 

I’m interested in a PCB with pins that go into the 9938 socket. 

[+FarmerPotato]

1 hour ago, Ksarul said:

Here are some 1.778mm round pin male header strips for you. . .and another one with a minimum buy of 1,000 parts. Here's another one on eBay. There are plenty of these listed on eBay, from multiple sellers.

That will be perfect!   I chose $23 for 20x40 from yixue, a seller I have bought from before. (Inexplicably uncommon 2x6 right angle male-female, aka PMOD connector.)

 

 

[+Ksarul]

I've bought from yixue before too--they are a reliable seller. . .especially for connectors.

[+dhe]

I want to try my question again.

 

Ricky, why would you want to piggyback a 9958, instead of just replace the 9938 in the socket?

[wierd_w]

If I read the initial question correctly,  the '38 has normal DIP pin separation, while the '58 has compact DIP separation.  The IC physically will not go in the prior's socket, and requires an adapter.

 

Additionally, there are other practical considerations for the innate differences between the chips and their featuresets to consider. ('tato specifically mentioned the colorbus, and PS/2 mice)

Edited April 30, 2021 by wierd_w

[+9640News]

6 minutes ago, wierd_w said:

If I read the initial question correctly,  the '38 has normal DIP pin separation, while the '58 has compact DIP separation.  The IC physically will not go in the prior's socket, and requires an adapter.

Is there any chance there may have been a 9958 variant in the 90's with normal DIP pin separation?  I would almost swear the 9958 I had fit the normal socket.

 

I do know I never got the circuit to work, and I gave the chip to someone else and later got feedback the chip was dead.  Whether I caused the chip to go bad, or I got a bad chip in the first place, I never knew which issue was the problem why what I had did not work.

[RickyDean]

32 minutes ago, dhe said:

I want to try my question again.

 

Ricky, why would you want to piggyback a 9958, instead of just replace the 9938 in the socket?

I wouldn't, but that may have been what @FarmerPotato had in mind, at least in my mind. Or at least when I responded.  since then there has been clarification. Sorry to befuddled and confuse.??

[RickyDean]

2 hours ago, 9640News said:

Is there any chance there may have been a 9958 variant in the 90's with normal DIP pin separation?  I would almost swear the 9958 I had fit the normal socket.

 

I do know I never got the circuit to work, and I gave the chip to someone else and later got feedback the chip was dead.  Whether I caused the chip to go bad, or I got a bad chip in the first place, I never knew which issue was the problem why what I had did not work.

As far as I no there is only the sdip 64 package, I have both, physically the same chip package.

Edited April 30, 2021 by RickyDean
add photo

[+Ksarul]

Both chips have always been in the SDIP package. I have never seen a standard DIP package for either one of them.