64K 400 upgrade

[Joey Z]

I have recently decided that enough was enough. I could not possibly go on without a 64K machine, so I upgraded my 400 (my only A8) to 64K. For those of you who wish to recreate what I did, this post is for you. Please read through this completely before you try it to get an idea of what it takes to do.

 

*****DISCLAIMER*****

I am not responsible for anything that happens because of this post. Good or bad. I don't care. I didn't do it. You use these directions at your own risk

 

Material Requirements

In no particular order:

• Atari 400 8 bit computer
  
  • You may be able to do this on an 800, by following these directions, although some of the info in this post will have to be figured out yourself then as far as where certain wires get soldered: http://www.atariage....ard-in-the-800/
    

  [*]Atari (it has to be the Atari one) 48K ram expansion upgrade for the 400

  [*]Plenty of wire

  • Stranded wire will probably work best, as far as the best size, your guess is as good as mine
    

  [*]Some method of building a permanent circuit (perf board, PCB, etc.)

  [*]One 7400 Quad NAND gate or other TTL level equivalent (LS, HCT, etc.) and matching socket, if you like

  [*]One 7402 Quad NOR gate or other TTL level equivalent (LS, HCT, etc.) and matching socket, if you like

  [*]Two .1uF capacitors, ceramic type

  • You may not need these, but it is a good idea and also good practice to use them
    

  [*]One blank 27C256 EPROM and method of programming it with a raw binary file

  • Alternatively, you can use an EPROM that is not blank and erase it before hand if you own a UV eraser
    

  [*]One DPDT switch

  [*]One momentary pushbutton, normally open

  [*]One 4.7Kohm resistor

  [*]Two 28 pin double wipe sockets, correct size to fit the EPROM

(socket in image is 24 pin, but shows the type you need. image taken from: http://www.soemtron....sktfacewipe.jpg)

• Soldering iron
  
• Solder
  
• A phillips head screwdriver
  
• Tape
  
  • Choose some variety you can write on and easily see what you wrote
    

  [*]Electrical tape (for insulating the solder side of your circuit board)

  [*]Writing utensil (pen, pencil, marker, crayon, feather quill, it doesn't matter)

  [*]Wire cutters

  [*]Wire strippers

  • You don't really need these, but they sure are nice to have
    

  [*]Hot glue or other potting compound (optional, but highly recommended)

Knowledge Requirements

• Soldering
  
  • If you don't know how to solder, you pretty much can't do this upgrade. Sorry.
    

  [*]Basic schematic reading

  • If you can't read a schematic, then I don't have any other way to describe this circuit to you really.
    

  [*]Basic circuit fabrication

  • Yeah, you need to know how to build a simple (2 chip) circuit. But you probably could have predicted that.
    

Step 1: Opening the Atari

Open your atari 400 being carful not to pull on the keyboard ribbon cable while doing so. For more detailed instructions (recommended if you are not familiar with the process) consult the Atari 400/800 Field Service Manual. (pg. 74, Atari 400/800 Field Service Manual)

 

Step 2: Installing the 48K Card

Install the 48K ram upgrade as per the instructions provided by Atari if you have not already. Verify that it works using the tests described in the installation manual.

 

Step 3: Building the Atari 400 64K Conversion Circuit Board

Build the circuit shown in the schematic diagram shown below: (click for bigger image)

 

Anywhere there is an input shown (like /S6) or an output (like /RAMEN) there will be a wire going from the circuit to somewhere else. NOTE: the switch is only shown for reference, do not mount the switch on your circuit, this switch needs to be mounted somewhere you can reach it. For now, leave the switch out completely. Also, do not forget about power pins. On the 7400 and 7402, the power pins are 14 (positive) and 7 (ground). You should install the .1uF capacitors across these pins (one on each chip) as well as connect the power pins of both chips together. This circuit board will be referred to as the 'Atari 400 64K conversion circuit board' from this point on.

 

Step 4: Modifying the 48K card

Remove the 48K ram board from the Atari 400 motherboard. It is time to make modifications to the 48K board. Start by completely removing R13. Next, remove U14 from it's socket and bend pins 3 and 6 outward so that they do not go back into the socket. Reinsert U14 and check proper orientation in the socket. Pins 3 and 6 should not be inside the socket.

 

Step 5: Attach the Atari 400 64K Conversion Circuit Board

In this step, you will begin wiring things together. Start by placing your Atari 400 64K conversion circuit board in the approximate position shown in the picture below. (the white thing with black electrical tape on it is the circuit board.)

 

Refer back to the schematic diagram from step 3. Connect the following connections from the schematic to the points indicated on the 48K board:

Atari 400 64K conversion circuit - Atari 48K RAM board

/RAMEN - bottom of empty R13 spot

A12 - U10 pin 14

A13 - U10 pin 2

A11 - U9 pin 14

 

In addition to these, connect the positive supplies of the two IC's to the top of the empty R13 spot. Connect the GND pins of the two IC's to the top side of C4 (or any other place a ground connection can be obtained). you will notice there are two wires not mentioned. the A14 and A15 lines. These two connections need to be able to reach to the left side of the motherboard, fold under, reach all the way to the underside of Z103 (pins 13 & 14 specifically) and still have a little slack. I had a jagged edge to the left of the ram slot on my 400 motherboard that left room for the wires to run between the motherboard and the RF shield. If you don't have this, you will have to figure it out yourself. Sorry.

 

This is a good time for a little tip. Unless you are trying to conserve wire, it is alright to use too much wire. you can always cut wire off. What is more difficult (and looks bad) is when you need to add more wire. So don't make the mistake I did several times, and use lots of wire if you are unsure.

 

Step 6: Wiring the Rest of the Atari 400 64K Conversion Circuit Board Wires

 

Start by bending the angle between your Atari 400 64K conversion circuit board and your Atari 48K board to be about 90 degrees. Insert the 48K board into the Atari 400 motherboard. In this step, you need to measure out the amount of wire you need to make each connection.

 

If you refer back to the schematic, you will see that we have 4 connections left: /S6, /S7, /ROMEN, and the line going from the DPDT to pins 5, 6, and 9 of the 7402. /S6 and /S7 connect to two more pins on Z103, so make sure the wires you connect will reach back. /S6 connects to pin 7 of Z103 and /S7 connects to pin 9 of Z103. /ROMEN will go to the general area of the OSROM's, A103, A104, and A105, but leave no wire connected here for now. The DPDT wire should be about long enough to extend an inch or two outside of where the front of the 400 normally is. After you are done wiring these wires, the back of your motherboard around the Z103 area should look like this (except hopefully you didn't use wire with PVC insulation that melted):

 

Step 7: Burn the EPROM

 

Grab the attached .bin file and burn it to your EPROM. Don't forget to put something opaque over the window in the EPROM after it has been programmed.

 

Step 8: Build a 27C256 --> Atari OSROM adapter

 

Now this bit I am not sure whether to be proud of or ashamed of. I unfortunately don't have pictures for this one, so you will have to use your imagination. Take the first 28 pin double wipe socket and bend pins 1, 2, 20, 22, 23, 26, 27, and 28 outward. insert this socket into the second socket. The sockets should form a stack, with the first one on top and the second one on the bottom. Bend the same pins outward (although you can omit 1, 2, 27, and 28 if you wish this time). Also, it is recommended you break those pins (1, 2, 20, 22, 23, 26, 27, 28) off of the second socket. Carefully solder wires to the pins you bent out on the first socket, skipping pin 1 to which a connection is not needed. Refer to step 9 to determine lengths for these wires. This whole thing is fragile, so I recomend using hot glue, or some other potting compound to seal up the connections, only after verifying you made good connections with an ohmeter.

 

Step 9: Wire the new OS ROM (27C256)

 

Start by removing the old OSROM's (A103, A104, A105) from their sockets. Take notes on which one went where. You should (ideally) store these in antistatic foam and keep them in a safe place. Take the OSROM adapter you built in step 8 and insert it into the socket that previously held A103. You should insert it so that pin 3 on the OSROM adapter is in pin 1 of the A103 socket. Take the wires you soldered on in step 8 and insert them into the following locations on the empty IC sockets. If you used stranded wires you may want to tin the wires before you do so.

OSROM adapter - motherboard socket,pin#

2 - A104, 21

20 - A104,12

22 - connect to /OSROM on the Atari 400 64K conversion circuit board

23 - A104, 18

26 - A105, 20

27 - this will lead to the DPDT switch, so this wire should be able to extend about an inch out of the front of the 400

28 - A104, 24

 

 

If you don't want all these wires just sitting in the socket like this, you can do one of two things:

1. route the wires to the backside of the board
    
   
2. remove the two sockets and solder the wires into the empty pads
   

Anyway, I am not proud of this method, I have decided, but it does work.

 

Step 10: Wire the DPDT and the reset button

 

For this step, reference the picture from step 9 when possible, otherwise, I don't have pictures for this step. First, you need to desolder the end of R142 that is closest to the back of the motherboard. this is a resistor close to the front of the board (seen in the upper left in the previous picture). The desoldered end of this resistor, as well as the pad it was in will go to the DPDT switch, so solder two wires, one from the resistor and the other from the empty pad. Next, attach a wire to the left side of R182, as shown in the previous photo. This will lead to the reset switch, also located in the front of the 400, so make this wire extend about an inch out the front of the 400. For the wiring of the DPDT switch, refer to the schematic shown previously. You want it so that in XL mode, the switch connects the pad that R142 used to be in to the Atari 400 64K conversion circuit board, and at the same time, it connects pin 27 of the 27C256 to 5v. 5v can be taken from pins 5 and 6 on the power supply connector (red in this photo). When it is in 400 mode, you want the pad where R182 used to be, to be connected to R142 (hmm, as it was when it was a normal 400...). at the same time, you want pin 27 of the 27C256 to be connected to GND. GND can be found on pins 3 and 4 of the power connector. Lastly, for the reset button, you want one terminal of your normally-open pushbutton to be connected to the left side of R182 and the other to GND.

 

Step 11: Test it

 

Put the 400 back together just enough to turn it on and check if it works. If you are in XL mode with no cartridge inserted and no SIO devices, the OS will try to boot SIO and eventually give up. It will then go to rainbow ATARI logo. If you are in 400 mode, under the previously stated conditions, the 400 will boot to memopad. If your 400 does not behave this way, immediately turn it off. Go back through these steps to find your mistake. Don't forget to check for shorts. If you didn't break the pins off on the second socket when you made the OSROM adapter, check for shorts between:

pins on the 27c256 - pins on A103

20 - 18

22 - 20

23 - 21

26 - 24

verify connections between:

3 - 1

4 - 2

5 - 3

6 - 4

7 - 5

8 - 6

9 - 7

10 - 8

11 - 9

12 - 10

13 - 11

14 - 12

15 - 13

16 - 14

17 - 15

18 - 16

19 - 17

21 - 19

24 - 22

 

I only mention this because I bent a pin underneath my adapter the first time I put it in on accident and that had me clueless for a while. Also, one of the pins that wasn't supposed to short, was shorting for some reason. I solved that problem by, you guessed it, breaking off the pin on the second socket.

 

Otherwise, if everything works, go on to step 12

 

Step 12: Finish Up

 

Start off by mounting the DPDT switch. I recommend mounting it above joystick port 3 or 4 because there are already holes here, these are he ones that cannot be used in XL mode, and normally you won't have a joystick connector in the way. I recommend you mount the reset button above the other joystick port. Make sure that your particular DPDT switch and pushbutton doesn't get in the way of the keyboard though. I if does, you will have to find another place to put the switch.

 

Cover the exposed wiring of your Atari 400 64K conversion circuit board with electrical tape to prevent shorts and bend it up against the 48K ram board.

 

Make sure all the wires are routed around the cartridge port. Next, put the RF shield back on. As long as you don't tighten it too much, the wires should be fine sandwiched between the board and the RF shield. I routed mine between the row of resistors and they seemed fine. From there, you basically follow the steps you took to take it apart in reverse.

 

Congratulations! You are now the proud owner of a 64K 400!

 

As an owner of a 64K 400, you can experience the best of both worlds being able to switch between XL mode and 400 mode. There are a few things to remember however. First of all, in XL mode, the third and fourth joystick ports do not work. Secondly, the normal console reset button does not work in XL mode. You must use the hard reset button that you installed.

 

Comments? Suggestions? Have a better way to make the OSROM adapter? Let me know.

Edited December 28, 2012 by Joey Z

[mimo]

So this gives full 64k xl compatibility?

 

How much do you charge?

[Joey Z]

So this gives full 64k xl compatibility?

 

How much do you charge?

 

Yes and no. This upgrade gives you XL OS and 64K which is probably enough to run most stuff. There are a few things that don't get added, like internal basic (although this can be emulated with a BASIC cart I guess), self test, etc. There are also numerous little changes elsewhere that really *shouldn't* matter (like RD5 goes to a GTIA trigger line I think on XL's). That particular example is known as the 'cartridge interlock' I think, so that the XL resets itself if you insert/remove a cartridge with the power on. But guess what our 400's already have? a cartridge interlock. You can't open the door without turning the 400 off.

 

As far as how much I charge: when I made this post I didn't intend to build the upgrades for anyone, but I guess I would have to think about that.

[Joey Z]

IMPORTANT: I screwed up the EPROM file. DON"T USE IT.

 

I wish I could edit the original post so I could fix that, but here is the new updated ROM that will work the right way. I wonder if an OP can do that for me.

 

This unfortunately means I need to open my 400 up again to correct this.

 

EDIT: for the 3 people who downloaded the broken ROM: if you haven't burned it already and you see this good. but if you already burned it, you can still save your ROM. I left the portion that was supposed the be the FP ROM as $FF so it is still 'blank'. if you were to take the first 2K FPROM of a 10K 400 OS ROM file, you could burn it to $2800 in the EPROM and have the FP corrected. on the other hand, it is only the FP that is screwed up, so pretty much, if you don't use basic (or other programming languages), you probably don't have much to worry about.

64K 400_27C256.bin

Edited December 28, 2012 by Joey Z

[Joey Z]

For those of you who wish to use alternate OS's or need a PAL OS's:

You will need three things:

The 400 OS you want to use.

The XL OS you want to use.

A hex editor.

 

First, open the 400 OS in your hex editor. It should be a 10K file (first 2K is FPROM and second 8K is OSROM). Next, create a new file in your hex editor. In that new file, create 6K (6144 bytes, $1800) of $FF. Using $FF allows you to make changes to this 'empty' space later on if you choose to do so. Copy and paste the whole 400 ROM after this 6K segment. Lastly, open the XL ROM and copy and paste the whole thing after the 400 ROM. Save it, burn it to your EPROM and you are done.

 

I forgot to mention in the first post, that this mod also gives you 4K of empty ROM to play around with in the $C000-$CFFF region.

[ClausB]

Cool.

 

Here's an alternative to the OS adapter: Bend out those pins on the EPROM itself (after programming of course) and plug it into the motherboard socket. Then cut the sides off a new socket, solder the wires to those, and plug them onto the outward bent pins of the EPROM.

[Charlie_]

For those of you who wish to use alternate OS's or need a PAL OS's:

You will need three things:

The 400 OS you want to use.

The XL OS you want to use.

A hex editor.

 

First, open the 400 OS in your hex editor. It should be a 10K file (first 2K is FPROM and second 8K is OSROM). Next, create a new file in your hex editor. In that new file, create 6K (6144 bytes, $1800) of $FF. Using $FF allows you to make changes to this 'empty' space later on if you choose to do so. Copy and paste the whole 400 ROM after this 6K segment. Lastly, open the XL ROM and copy and paste the whole thing after the 400 ROM. Save it, burn it to your EPROM and you are done.

 

I forgot to mention in the first post, that this mod also gives you 4K of empty ROM to play around with in the $C000-$CFFF region.

 

Congrats on the upgrade Joey. Sounds really cool. Well done.

[+Stephen]

Nice job on this Joey.

[Joey Z]

Cool.

 

Here's an alternative to the OS adapter: Bend out those pins on the EPROM itself (after programming of course) and plug it into the motherboard socket. Then cut the sides off a new socket, solder the wires to those, and plug them onto the outward bent pins of the EPROM.

 

I thought about bending the pins on the EPROM but I wanted to be able to remove the EPROM should I have to, and look at where I am now. I need to pull the thing out to fix the FPROM in 400 mode. guess it was a good thing I did it this way.

[Roydea6]

IMPORTANT: I screwed up the EPROM file. DON"T USE IT.

 

I wish I could edit the original post so I could fix that, but here is the new updated ROM that will work the right way. I wonder if an OP can do that for me.

 

This unfortunately means I need to open my 400 up again to correct this.

 

EDIT: for the 3 people who downloaded the broken ROM: if you haven't burned it already and you see this good. but if you already burned it, you can still save your ROM. I left the portion that was supposed the be the FP ROM as $FF so it is still 'blank'. if you were to take the first 2K FPROM of a 10K 400 OS ROM file, you could burn it to $2800 in the EPROM and have the FP corrected. on the other hand, it is only the FP that is screwed up, so pretty much, if you don't use basic (or other programming languages), you probably don't have much to worry about.

Why did you chose the 1200xl version 10 rom to put into this Atari 400?? Is this better than using an 800xl rom..

[Joey Z]

Why did you chose the 1200xl version 10 rom to put into this Atari 400?? Is this better than using an 800xl rom..

that way it doesn't crash and burn when it realizes there is no self test. but that was the excuse I thought of after I realized what I had done.

[Roydea6]

But the 1200xl has a self-test also.. I beleive that pressing the Select key while the Rainbow is on screen will bring up the self-test feature..or during boot.

[+MrFish]

But the 1200xl has a self-test also.. I beleive that pressing the Select key while the Rainbow is on screen will bring up the self-test feature..or during boot.

 

<Help> key, during rainbow screen...

Edited December 29, 2012 by MrFish

[Joey Z]

But the 1200xl has a self-test also.. I beleive that pressing the Select key while the Rainbow is on screen will bring up the self-test feature..or during boot.

and maybe it does, but it doesn't go directly to it. anyway, I just picked pretty much the first XL OS ROM in the selection.

[sup8pdct]

Some 20 odd years ago, I modded the XL os to enable the 400/800 nmi reset. I just had to wipe out the id and date bytes at the begining of the rom and make small change to how pointer was set up. Don't know if i still have that file.

 

James

[Defender II]

Some 20 odd years ago, I modded the XL os to enable the 400/800 nmi reset. I just had to wipe out the id and date bytes at the begining of the rom and make small change to how pointer was set up. Don't know if i still have that file.

 

James

Please post if you find it.

[AtariMagic!]

Please post if you find it.

 

i would want to see the file too

[adamchevy]

Would this upgrade allow me to play Tempest Elite on a 400? I almost purchased an 800XL, but they are so ugly to me. Or did Candle ever make an Upgrade like the incognito for the 800?

Edited September 22, 2018 by adamchevy

[+slx]

Would this upgrade allow me to play Tempest Elite on a 400? I almost purchased an 800XL, but they are so ugly to me. Or did Candle ever make an Upgrade like the incognito for the 800?

Not yet, although he remarked on such a thing years ago. Wouldnt hold my breath waiting for it. Edited September 23, 2018 by slx

[+DrVenkman]

Would this upgrade allow me to play Tempest Elite on a 400? I almost purchased an 800XL, but they are so ugly to me. Or did Candle ever make an Upgrade like the incognito for the 800?

 

 

Not yet, although he remarked on such a thing years ago. Wouldnt hold my breath waiting for it.

 

Um, the Ultimate 1MB?

[flashjazzcat]

I think he's asking if Candle ever made an Incognito for the 400. The answer is no. Ultimate 1MB is XL/XE only.

[+DrVenkman]

I think he's asking if Candle ever made an Incognito for the 400. The answer is no. Ultimate 1MB is XL/XE only.

 

It wasn't apparent to me what he meant, as the post I quoted referenced the 800XL. *shrug*

[+slx]

 

 

 

Um, the Ultimate 1MB?

 

No, candle posted about an "Ultimate-like" or "Incognito-like" device a couple of years ago. No details, didn't find anything about it since.

[flashjazzcat]

 

It wasn't apparent to me what he meant, as the post I quoted referenced the 800XL. *shrug*

 

Heh... well, he said he wanted to play Tempest Elite on his 400, added that he didn't purchase an 800XL and that he wanted something like the Incognito. So I figured he wanted something like the Incognito for a 400.

[adamchevy]

 

Heh... well, he said he wanted to play Tempest Elite on his 400, added that he didn't purchase an 800XL and that he wanted something like the Incognito. So I figured he wanted something like the Incognito for a 400.

That’s exactly right. It looks like I’ll have to end up purchasing an XL/XE system of some kind to play Tempest Elite. Unless I want to do some crazy modding of a 400 that involves cutting traces and a large amount of soldering.