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A few years ago I searched for an OS switch solution to support alternative OS versions for the SIO2BT project

and I found the following web page created by Igor Gramblička:

http://blog.3b2.sk/igi/post/Vymena-ATARI-OS-1_2-Change-ATARI-OS-1_2.aspx

One can use a stripboard or even bend the EPROM pins (which I did) to achieve the goal.

 

Recently I asked Mr Robot for designing the board with KiCad and he kindly agreed.

With his permission I would like to share his magnificent results here:

 

[attachment=615176:msg-62759-0-70844300-1547668242.png]

[attachment=615178:msg-62759-0-79341200-1547668266.png]

[attachment=615179:msg-62759-0-96267100-1547668249.png]

 

The Gerber files:

[attachment=615177:4XOS.zip]

 

For a few dollars you can order a set of ~10 boards at:

http://dirtypcbs.com/store/pcbs

 

You just need two 4k7 resistors, PIN headers, IC socket, 27C512 EPROM and external switch(es) to build your own OS switch.

 

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Very nice and compact. Maybe it could be slightly improved by having the top socket offset to the other side of the underside headers, to allow more room if next to a similar adapter in the BASIC socket on an 800XL?

 

I tried this recently, and got dropcheck's 4-in-1 OS adapter to fit next to the RetroInnovations 2364 up-to-8-in-1 adapter, but only by using an extra socket to offset the height of PCB's: http://atariage.com/forums/topic/284992-does-atarimax-take-paypal-a-fork-of-the-old-steve-takes-ages-to-reply/?p=4164363

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Good point, here's a new version with the pins moved over and the board trimmed along that edge as close as it can be. 

 

[attachment=615264:Screenshot 2019-01-17 at 15.57.31.jpg]

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I have a circuit (heretofore untested) that uses three pull-down resistors and two NOR gates from a 74LS02 TTL chip that will allow the use of a single pole 4-way switch (rotary or slide switch) for OS selection instead of the 2-bit binary switching.  It uses a 4 to 2 encoder circuit with NOR gates.  Position #1 is open (NC) because the three inputs on the encoder are pulled down.  As a result, in position #1 pins A15/A14 on the eprom are set High/High.  When switching to positions 2, 3 or 4, either A15/A14 are High/Low, Low/High or Low/Low.

 

I need to acquire an eprom programmer or at least the temporary use of one, before I can build the circuit and test it but I'm over 99% certain that it will work as designed.

 

I think it might be possible to nest the 74LS02 inside the socket area of the board above or one similar, along with the three resistors for the 4 to 2 encoder.  No pull-up or pull-down resistors are needed for the eprom pins because the 74LS02 provides the distinct logic states needed by the pins.

 

Has anyone else considered something similar to eliminate the need for the pair of binary selector switches?

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I was trying to figure this out as well, how to use a simple 4-position slider switch to choose between the four. This was for Dropchecks version, which had 3 pins for each switch, which has a seemingly unnecessary 'NC' pin...  Also, when wiring to the switch, only one GND lead is needed.. so only 3 wires total running from the switch to the adapter are really required.
 
I came up with one drawing based on a 2-pole, 4 position switch that has two 'inputs' on one end, and another variation that put the 'inputs' in the middle...
 
 [attachment=633953:4in1-B.png]
 
This one has the 'input' in the middle, but depending on the switch, it may be at one end.
 
[attachment=633956:middle-switch.png]
 
Some pics of an implemented version, but with 2 GND wires to the switch. (Could have just used 1, and bridged to the other side, for 3 wires total to the ROM adapter)
 
[attachment=633954:52634635_573781343101631_281963533535543296_n.jpg] [attachment=633955:switch.jpg]
 
Another variation is a 4 position slider switch that has a BCD style coding, i found a description of the switch wiring here:
 
https://forum.arduino.cc/index.php?topic=398157.0

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Using the NOR gates (or OR gates) will eliminate the need for the second pole on the switch, simplifying the wiring to the switch considerably.  The OR and NOR will be inverted results (1234 vs 4321),

 

  • One of the inputs of each OR or NOR gate will be connected together and connected to position #4.
  • The other input for each OR or NOR gate will go to either position #3 or #2 respectively.
  • Position #1 is "NC"
  • The leads to #2, #3 and #4 switch positions should be pulled DOWN via suitable value of resistors (3.3K, 4.7K, etc)
  • Output of one OR or NOR gate goes to A15 and the output of the other one goes to A14.

This means with four wires to the switch (three inputs and one +5v), one can switch between four separate OS's.

 

Edit: I forgot to mention that in my circuit design, the other four inputs for the other two gates are tied to ground so they aren't floating.

Edited by Waynetho

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Upon reflection, I see that the DP4T switch option gives a more streamlined approach than my 74LS02 solution.  The DP4T chip method only requires three wires and two pull-down resistors and no additional circuitry (74LS02).  The NOR or OR gate solution makes the switch more logical in it's hookup but it requires more components to make it work.

 

Additionally, it will work with the board that is already in this thread rather than creating a new board with the logic circuitry.

 

I bow to a more elegant design. ;-)

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Interesting side story about a conversation I had with Wes Newell in the mid '80's regarding my plans to make a triple OS board similar to his Ramrod XL.  He told me it would be impossible to make a 3-OS board unless I could source the special three position switch (ON-ON-ON) that he used with his board.

 

I proved him wrong.  I used a PULL-UP resistor for the CS pins on the first and third chips, and a PULL-DOWN resistor for the CS on the middle chip.  I used a DPDT "Center-OFF" switch to GROUND either #1 or #3 chip's CS in their respective switch position, along with pulling the middle chip's CS "HIGH" when in either "ON" position.  In the CENTER-OFF position, the board defaulted to the #2 chip active due to #1 and #3 being pulled HIGH and the #2 chip being pulled LOW by resistors.  The switch used five wires (CS-1, CS-3, GND, and CS-2, +5V).

 

This was accomplished with a switch readily available from Radio Shack.  For the record, I didn't mass-produce the board or even give it a name.  I made one for my 800XL and I believe two more for friends, all hand-wired.

 

I wish we had 27512 chips and the mod discussed in this thread back then as the OS daughter board required three separate 16k OS chips.

Edited by Waynetho

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I've got a 16 in one OS in one of my XLs. One EPROM, a hex encoded thumbwheel switch, wire and a few resistors.  No board needed (although I should have built one for it).  Those SCSI select switches work great for an 8 in 1!

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@JR> i like the sound of that setup?

 

what parts are required?

any pics?

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Pretty simple really, 27c020 EPROM, 4 pull up resistors for the additional address lines.  The 4 encoded lines from the switch to toggle the 4 address lines. Pin compatible with the 27c128, so it just plugs in the OS socket with the extra pins hanging over the end, and one or 2 of the pins not going in the socket. Tap ground and +5v somewhere and wire it all up.  I think I plugged the pins that didn't go in the original socket into some SIP socket and soldered to that.

 

I'll try to dig it out and get some pictures soon.

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Hi,

 

What other Atari OSes that one can put on with this board?  Would appreciate links or even download links.  I would like to try out this new OSes and see what they are/how they function.

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Hi,

 

What other Atari OSes that one can put on with this board?  Would appreciate links or even download links.  I would like to try out this new OSes and see what they are/how they function.

 

 

Saw the below at https://www.atariarchives.org/mapping/appendix12.php

 

"Probably the most elegant solution is the XL BOSS board which allows you to switch in a RAM OS, the older 800 OS, and the XL OS,

as well as turn BASIC on or off with a few keypresses. It's available from Allen MacroWare in Redondo Beach, California.

"

Edited by unebonnevie

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