Interesting modded XEGS

[GreyHobbit]

I picked up an modified XEGS from eBay.  It has two knobs on the top, one labelled CUPID; ATARI; 800 O/S, and the other labelled MISSILE; GLAXIAN; BASIC; EDITOR.

 

The CUPID label interested me, I used to have a ComputerHouse card in a 130XE with a CUPID parallel printer interface, so I kind of hoped there might be a ComputerHouse card in this XEGS.  Sadly it appears not, but there are 25-pin connectors on the back labelled 'Modem' and 'Printer'.  As the first knob looks like an OS selector, I'm guessing it has an OS modded for the CUPID interface, a stock XE OS and the 800 OS-B ROM.  The other knob must select ROMs in the cart area.  (Although the cart select appears to do nothing if the ATARI OS is selected, it only boots to Basic and a READY prompt.  The 800 O/S option only boots to a screen prompting to boot from disk or cassette.  With the OS set to CUPID, the cart selector chooses between Missile Command, Galaxian, Basic and the Assembler/Editor, but with a custom font.)

 

Anyway, when I lifted the lid, someone has clearly spent a lot of effort on this!

 

Look at those stacked EPROMs!

 

Looks like the RAM has been expanded and two pins on Freddie have been lifted and connected elsewhere

 

I'm not yet sure what's going on here.  What chips are piggybacked here and what might be the purpose of this?  I think some of the wires trace back to the mod on the Freddie chip.  Is it something to do with the memory upgrade?  I assume it's been upgraded to 128kB but I haven't got running a sysinfo program to check.

 

There's a veroboard above the SIO port, I can't see the components as it's soldered to the shield and connected through to the 25-pin connector labelled 'Modem' so I'm guessing it's an R-verter type RS232 mod.

 

There's an MC6821 piggybacked on the PIA (I think) connected to the Printer port.

 

This only arrived in the post yesterday and I've had no time to do much other than plug it in and confirm that it appears to work fine, lift the lid and take these photos.

 

I'll have to try to dump the ROMs for the CUPID/ATARI/800OS options and see if they can be identified.  But as I have neither a modem nor a parallel printer anymore it's probably more of a curiosity than anything, but I got it for about £140 and looking at others on eBay I think that's reasonable enough.

 

I might have to do something about the video output, it's not great...

 

Geoff

[TGB1718]

At first glance, it looks like he's using the PAI chip to drive the printer port, I made a similar device bitd but

mine plugged into the joystick ports, the driver was loaded into page 6 and could drive most Epsom compatible

printers of the day.

 

It may be that he's modified the 800 OS ROM to have the driver built in, so a dump of the 800 ROM would be

nice whenever you can dump it to see if it's done that way.

 

As for the RS232 port, can't see enough, but it would have required +/-12Vdc to drive it, so maybe that PCB has

some sort of convertor 

 

I notice also apart from all the blue wires, there's a piggy backed TTL chip of some sort there too

[BillC]

1 hour ago, TGB1718 said:

As for the RS232 port, can't see enough, but it would have required +/-12Vdc to drive it, so maybe that PCB has

some sort of convertor 

While the original RS232 specification called for +/- 12V signalling this was later revised to allow TTL level(0V/+5V) signalling. In the mid 80's I purchased a SUPRA 2400 BAUD modem that came with an R-Verter interface which uses TTL signalling.

[+mytek]

9 hours ago, TGB1718 said:

As for the RS232 port, can't see enough, but it would have required +/-12Vdc to drive it, so maybe that PCB has

some sort of convertor 

Not if they used a MAX232 or a variant of such. These TTL-to-RS232 transceiver chips have been around for over 20 years and have built-in charge pumps to create the required +/- voltages for Rs232.

 

Edited May 8, 2022 by mytek

[Rybags]

Interesting... I imagine with half or all of the shielding removed to fit that stuff + all the extra wires running around the video would have been affected.

In the modern day all that Rom multiplexing could be done a lot easier.  But if it works, why not stick with it.

[TGB1718]

10 hours ago, mytek said:

Not if they used a MAX232 or a variant of such. These TTL-to-RS232 transceiver chips have been around for over 20 years and have built-in charge pumps to create the required +/- voltages for Rs232.

That's the sort of thing I meant, just couldn't remember the name of it (I have one in my original SIO2PC) built way back in time

 

[1050]

Your memory has been upgraded and you don't need a sysinfo program to check it, the built in self-test will show four larger bars at the bottom of the standard memory test screen when it's done with the standard ram test with the smaller green or red squares. Those larger blocks underneath the standard display indicate one 16K bank window each, but the original code for that test is defective and it only shows two repeated blocks as the four and only the two banks are thus "tested". This extended memory test (defective as it is) was the last OS version used for 130XE so was included in the XEGS as is, even though the stock XEGS doesn't have extended memory usually - the code for it is still there and if extended memory is not detected, then the memory test code just cycles back to the beginning to start all over again. Just like it also does when extended memory is detected and the code does the four bars at the bottom, it also ends with a jump back to the start to repeat the testing.

[GreyHobbit]

I have had almost no free time lately to do any further investigation with this XEGS yet, but I did use the Atari ROM Checker by JAC! to dump the three OS ROMs.  The Atari ROM is unsurprisingly identified as Atari OS Rev 4 1987-05-07.  The other ROMs show as Unknown.  They initially report the checksum as incorrect and rescan with the checksum fixed.  Both the correct and incorrect checksum versions for both ROMs are reported as Unknown.

 

The dumps are attached in case anyone is interested in examining them.

 

Aside from the slightly wonky video output (although I am running it through a cheap AV2HDMI converter which probably doesn't help) I'm finding the XEGS to be a lot more fun than I expected, the detachable keyboard is nice although it might be better with a curly phone-type cord to give it a bit more flexibility and reach.

 

I assume all the mods in this particular XEGS will make it a nightmare to get to a state where I could install a U1MB?

 

Geoff

 

800OS.ROM

CUPIDOS.ROM 

 

Edited May 22, 2022 by GreyHobbit

[doctor_x]

This is very cool. Would love to know what he used the high speed rs232 port for.. meaning curious if this was a BBS Atari XEGS or if he was using it for dialing out, was a developer of some atari modem utility, or what?

 

thanks for sharing!