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JoSch

XEGS keyboard on a 400

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I'm thinking about connecting a XEGS keyboard to my 400.

Since the XEGS keyboard has two 4051 in its case, the signals on the connector are essentially the POKEY input signals.

My thinking is that I only have to connect the XEGS keyboard signals to the POKEY.

My question: Should I protect the POKEY or does it suffice to directly connect them?

 

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Why didn't I think of that myself?

 

My 400 keyboard is broken and was looking to add a 600XL keyboard to it but found no good solution to case the keyboard (except for keeping it in the 600XL itself). I totally forgot about the XEGS keyboards I've laying around, albeit those haven't got the Start/Select/Option/Reset keys.

 

I'd guess you can hook it up directly to the POKEY but you can compare the schematics to be sure.

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XEGS has inductors between the keyboard lines and external port - these aren't present on other machines where a direct connection exists to the multiplexor ICs (aside from some lines which appear to have pullup resistors).

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This would make a nice project for some to sell. Maybe some kind of adapter board with a XE keyboard cable female plug. I'd love to have one of these. You would still have to use the Start, Reset, Select and Option keys on the 400 keyboard but that's not a big deal. Just place the XE keyboard right in front of the 400.

 

Allan

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Why didn't I think of that myself?

 

My 400 keyboard is broken and was looking to add a 600XL keyboard to it but found no good solution to case the keyboard (except for keeping it in the 600XL itself). I totally forgot about the XEGS keyboards I've laying around, albeit those haven't got the Start/Select/Option/Reset keys.

 

I'd guess you can hook it up directly to the POKEY but you can compare the schematics to be sure.

Is the keyboard itself broken or do keypresses don't register?

 

 

 

You would still have to use the Start, Reset, Select and Option keys on the 400 keyboard but that's not a big deal. Just place the XE keyboard right in front of the 400.

 

Allan

To sometimes press the function keys on the 400 keyboard doesn't look that bad to me ;-)

Another possibility is to modify the XEGS keyboard and route the function keys to their signals. Such a modification is hinted at in the schematics of the Transkey-II-XEGS.

Edited by JoSch

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XEGS has inductors between the keyboard lines and external port - these aren't present on other machines where a direct connection exists to the multiplexor ICs (aside from some lines which appear to have pullup resistors).

I'll look at that. Since we're in the process of moving my Atari stuff is packaged away at the moment.

At the moment, I just want to think about that project. Doing it will have to wait until my workplace is set up.

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This would make a nice project for some to sell. Maybe some kind of adapter board with a XE keyboard cable female plug.

 

Allan

Perhaps a Transkey variation?

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I'm thinking about connecting a XEGS keyboard to my 400.

Since the XEGS keyboard has two 4051 in its case, the signals on the connector are essentially the POKEY input signals.

My thinking is that I only have to connect the XEGS keyboard signals to the POKEY.

My question: Should I protect the POKEY or does it suffice to directly connect them?

 

 

Yes this will work, and is pretty much what TransKey does. Basically you are paralleling all of the POKEY keyboard related lines (K0-K5, KR1, KR2). Both the 400 and the XEGS keyboard have 47K pull-ups on the KR1 and KR2 lines, which will drop to approximately 23K in parallel, but that shouldn't be a problem for the key matrix signals that pass through the 4051's to pull low. As far as protecting POKEY, the only real concern would be ESD, but that would likely not be a problem if you left the keyboard plugged in, and only a concern when it was unplugged and you touched the D-Sub 15 jack on your modified 400 after sliding across the carpet. I think the risk is very low.

 

BTW, your internal membrane keyboard would still work as well, and could be left plugged in. Well that is if it were a 'good' working membrane keyboard, which your's apparently is not. Should still be ok to leave it plugged in, so long as whatever is wrong with it is not shorting out any of the keys in the matrix.

 

 

Another possibility is to modify the XEGS keyboard and route the function keys to their signals. Such a modification is hinted at in the schematics of the Transkey-II-XEGS.

 

Yes what was suggested for TK-II console switch signal feed through modification would allow you to pass those signals into the XEGS keyboard, but you would still need to supply the switches and figure out how and where to mount them. However it would also make you more compatible for a future TK-II-XEGS board to be plugged in, if you decided to go that route later on.

 

5678685.jpg

TK-II-XEGS-S (2nd variation in XEGS series)

 

This one can optionally be mounted internal to the Atari if so desired, or simply plugged into an XEGS.

 

 

- Michael

Edited by mytekcontrols

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Yes this will work, and is pretty much what TransKey does. Basically you are paralleling all of the POKEY keyboard related lines (K0-K5, KR1, KR2). Both the 400 and the XEGS keyboard have 47K pull-ups on the KR1 and KR2 lines, which will drop to approximately 23K in parallel, but that shouldn't be a problem for the key matrix signals that pass through the 4051's to pull low. As far as protecting POKEY, the only real concern would be ESD, but that would likely not be a problem if you left the keyboard plugged in, and only a concern when it was unplugged and you touched the D-Sub 15 jack on your modified 400 after sliding across the carpet. I think the risk is very low.

 

BTW, your internal membrane keyboard would still work as well, and could be left plugged in. Well that is if it were a 'good' working membrane keyboard, which your's apparently is not. Should still be ok to leave it plugged in, so long as whatever is wrong with it is not shorting out any of the keys in the matrix.

 

Thanks for the explanations. But I think, that the resistance (is this the correct word?) will only drop to 23kOhm, if both corresponding KRx line will be signaled. So I would assume, that in the normal of using only one keyboard at the same time, it would be okay.

BTW, my membrane keyboard is working, but it's a membrane keyboard ;-)

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Thanks for the explanations. But I think, that the resistance (is this the correct word?) will only drop to 23kOhm, if both corresponding KRx line will be signaled. So I would assume, that in the normal of using only one keyboard at the same time, it would be okay.

BTW, my membrane keyboard is working, but it's a membrane keyboard ;-)

 

The change in resistance (yes that was the correct word) is an unavoidable characteristic of paralleling the two pull-ups (one side to KRx and the other side to +5V). And since they are identical values (47K each), the end result = 1/2 the value, or 23.5K. This resistance is present to create a more solid logic '1' state (+5V) and when pulled low by the keyboard will ideally go to a logic '0' state (GND). Of course the lower the pull-up resistance, the harder it will be to pull it all the way down to GND. So depending upon the situation, you might be a few to many millivolts shy of GND. In most cases and especially with low speed logic, being a tiny bit above GND is still within the operating window of the particular IC chip. And I think that will also hold true in this case as well. So I wouldn't worry about it. I just mentioned it, because it was something that would occur by paralleling the two devices (400 and XEGS keyboard).

 

- Michael

Edited by mytekcontrols

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You're correct.

I hadn't considered, that you mentioned pull down logic.

I was thinking pull up.

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You're correct.

I hadn't considered, that you mentioned pull down logic.

I was thinking pull up.

 

The resistors are the 'pull-up' aspect, and the key matrix will provide the 'pull-down' in the event of a key closure. Part of the reason this was done, is that the 4051's are in essence an 'analog' rotary switch, so they don't have any fixed logic level to speak of (they neither pull-up or pull-down) and simply pass a signal through. The only logic level aspect of a 4051 is the address lines which in essence determine the position of the 'rotary' switch (which of the 8 inputs gets routed through to the single output). So one of the 4051's has that input tied to GND, and the other one is tied to KR1 on POKEY (the 4051 switch is bi-directional just like a real mechanical switch). Depending upon how the 4051's get addressed (also by POKEY), a single cross point in the key matrix is selected. If that cross point is shorted (by pressing the associated key) then the GND (or logic '0') signal gets routed through to KR1. Since POKEY knows where its address counter is, it also knows what key has been pressed when it sees the logic low condition appear on KR1. But in the scenario where no key is pressed, we need this line to go high (+5V). That is the purpose of having the 'pull'up' resistor to +5V, since otherwise KR1 would see a floating state which could be anywhere between +5V and GND which is not a good thing (causes ghosting, as in false key presses).

 

1598881_orig.png

 

 

I hope I haven't bored you to death by all this technical info :sleep:

 

- Michael

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I hope I haven't bored you to death by all this technical info :sleep:

 

- Michael

No, you didn't, but I knew this stuff ;-) I had read the 400 schematics, so that I could connect a 800XL keyboard to the 400.

 

Quick aside: I did enough electrical engineering in university so that I can follow you, but I don't practice it much, because I'm a developer by trade.

 

What I meant, when I did my remark on the two resistors, was that I thought if a key is pressed the 4051 lines get connected to 5v. As you correctly stated, they get connected to GND, so KRx gets pulled down.

 

Can you think of a way to avoid problems?

Edited by JoSch
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No, you didn't, but I knew this stuff ;-) I had read the 400 schematics, so that I could connect a 800XL keyboard to the 400.

 

Quick aside: I did enough electrical engineering in university so that I can follow you, but I don't practice it much, because I'm a developer by trade.

 

What I meant, when I did my remark on the two resistors, was that I thought if a key is pressed the 4051 lines get connected to 5v. As you correctly stated, they get connected to GND, so KRx gets pulled down.

 

Can you think of a way to avoid problems?

 

There is absolutely no problem with having the parallel keyboards, and it should work just fine. On the original 1990 TransKey it too had its own 47K pull-ups and I never ever saw a problem with this (whatever problems that original TransKey had were likely related to the firmware). On the latest iteration TK-II, I eliminated the pull-up resistors. Not because of any problems, but just to minimize components and allow for a very small form factor. On Atari's that have the pull-ups incorporated into the keyboard (1200XL & XEGS), I provided a means to set TK-II's KRx outputs to be active TTL logic and not float.

 

If you don't mind me asking, what kind of developer are you?

 

- Michael

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Is the keyboard itself broken or do keypresses don't register?

 

To sometimes press the function keys on the 400 keyboard doesn't look that bad to me ;-)

Another possibility is to modify the XEGS keyboard and route the function keys to their signals. Such a modification is hinted at in the schematics of the Transkey-II-XEGS.

 

Sticky "keys" are the problem. Some register too much :-)

 

Function keys...

Yes, it's possible to add those that way but it requires modification to the keyboard casing. I'd at first prefer to leave it visually unmodified and at second, there isn't much space in the casing to place some custom keys. Most of the internals are covered by the membrane which is, IIRC, bigger then required because the functions keys are actually in the membrane layout (it's the same as from a regular XE keyboard) and you can't remove/cut it because there are traces over there.

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Sticky "keys" are the problem. Some register too much :-)

 

I bought two 400 keyboards off Ebay once, but I haven't tested them yet. At the moment, they are stored away until the move is complete. If both work, I could part with one of them. PM me and we can make a deal if you like.

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If you don't mind me asking, what kind of developer are you?

 

- Michael

I'm an application developer. At the moment, I'm mostly doing web application stuff.

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My suggestion would have been just ditch the 4051s and patch in your new interface there...

 

With the pullups, you'd probably just get away without using any at all with the second mux pair a parallel install. They're present to keep the logic level going to Pokey at 1 unless otherwise desired, not for the benefit of the multiplexors.

Edited by Rybags

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My suggestion would have been just ditch the 4051s and patch in your new interface there...

 

With the pullups, you'd probably just get away without using any at all with the second mux pair a parallel install. They're present to keep the logic level going to Pokey at 1 unless otherwise desired, not for the benefit of the multiplexors.

 

Actually nothing needs to be changed or ditched on the original 400, just add add a male D-Sub 15 jack and tie it into POKEY K0-K5, KR1, KR2, Vss (GND), Vcc (+5V) as shown below. All connections can be made from below the POKEY socket, on the bottom-side of the Atari motherboard. If you plan on later using a TK-II-XEGS, then make the connections shown in RED to the appropriate console switch connections. And the nice part is, that your internal keyboard will still work as well.

 

OlWpdfN.png

 

- Michael

Edited by mytekcontrols

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Almost forgot :roll:

 

If you do add the optional console switch connections to the D-Sub 15 Jack (see previous post), then it will be necessary to make a quick no-solder mod to the XEGS keyboard. Basically you need to open it up and cut two wires as shown below.

 

1863230_orig.jpg

 

This doesn't harm the XEGS keyboard in any way, but simply allows the connection points where those wires go to be used for two of the console switch connections. They are a second set of redundant +5V and GND wires. And just so you know, this keyboard will still work perfectly alright on a stock XEGS after the modification.

 

- Michael

 

 

EDIT: If you check out that photo you'll see something rather interesting in the upper right corner. Yes that's right you're seeing where the console switches were originally planned to go, but in the end never did, which is unfortunate.

Edited by mytekcontrols

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EDIT: If you check out that photo you'll see something rather interesting in the upper right corner. Yes that's right you're seeing where the console switches were originally planned to go, but in the end never did, which is unfortunate.

I knew it shared the mylar with the 65/800/130XE keyboards but kind of forgot that also the mechanical part of the keys were actually there. Now I'm curious if it's possible to fit the original key caps from the XEGS main unit into the keyboard when making the required holes. It should be no problem to get the right raster lines from the keyboard PCB.

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I knew it shared the mylar with the 65/800/130XE keyboards but kind of forgot that also the mechanical part of the keys were actually there. Now I'm curious if it's possible to fit the original key caps from the XEGS main unit into the keyboard when making the required holes. It should be no problem to get the right raster lines from the keyboard PCB.

 

No the buttons on the console are an entirely different design, tall and centered over the actual recessed switches, whereas the keyboard HELP button is offset and quite different in construction (low profile). Most likely the extra switches in the keyboard are usable but not presently hooked up to anything other than the Mylar trace connection block on the controller board. So if you wanted to use them, you would first have to figure out what to use for the buttons (more HELP buttons with new label?), and then make the necessary connections from the Mylar connector to the points I showed in the previous drawing. If somebody needs a keyboard to experiment on, I have an extra that I would provide for free to someone in the USA that really intends to try this (PM me if interested).

 

- Michael

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The only reason the console switches are there is because it's the exact same keyboard used in later model 65/130XEs. I doubt there was ever any intention to keep the console keys on the detachable XEGS keyboard, but it would have been a good idea all the same. Lots of serious applications require console key input.

Edited by flashjazzcat
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No the buttons on the console are an entirely different design, tall and centered over the actual recessed switches, whereas the keyboard HELP button is offset and quite different in construction (low profile).

 

I fail to see the issue. Anything is possible with some smart cutting and a bit of glue :-)

 

XEST Case 01

XEST Case 03

 

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I fail to see the issue. Anything is possible with some smart cutting and a bit of glue :-)

 

What exactly is that? Hmm... now you got me curious :ponder:

 

But yes with the right skills and determination anything is possible.

 

- Michael

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