For more information please visit the original website of this project:

https://ataribits.weebly.com/ram.html

1200XL-1mb   1MB Solder-Less Upgrade for the 1200XL

A Plug 'n' Play fully SRAM 1088K upgrade for the 1200XL, which not only expands the system memory to a whopping 1088K, but also kills much of the noise associated with the original DRAM, thus enabling noise-free video output.

By piggybacking 4 existing chips on the 1200XL motherboard (MMU, Decoder, CPU, PIA), all the required logic signals are easily acquired. Thus allowing for a completely solder-less memory upgrade, with full reversibility. No modification other than removal of an RF choke used only by the RF sound section is necessary, assuming it can't be bent over to clear the top part of the board. If you have no plans for RF output, simply cut the choke out of circuit.

Presently there is no BOM, so reference the schematic for the necessary components, which can be easily gotten from Mouser or Digi-Key (the 0.1uF capacitors have 0.2" lead spacing, and the 3K resistors are standard 1/4 watt rated).

1200XL-1mb_schema_v1.2.pdfDownload File

Schematic ONLY

No BOM

1200XL_1mb_v1.2_gerbers.zipDownload File

68.1 x 102.4 mm

2-Layer PCB

1 mm Thickness !!!

1200XL_1mb.jedDownload File

 EMMU JED Flashed to ATF22V10C-15PU PLD

Thanks goes out to Jurgen (AtariAge member tf_hh) for his great design and contribution of the 1MB EMMU jed file that makes this project possible.

All IC sockets used for piggybacking (U5, U6, U7, U9 on the 1200XL-1mb PCB) need to be machine pin type, with an extra socket stacked underneath.

The exception is the MMU (U5) which requires an offset pair of Male-to-Male machine pin headers (MMU-P1) to allow interception and re-routing of key signals.

(Amazon LINK to machine pin header)

After installing this board, all 4 of the original 1200XL chips that were removed need to be transferred to the top side.

There are two jumper blocks present. For most situations the top one should be set to 1MB (left = 1MB / right = 512K), and the bottom one will be shorted for Extended Memory support (open = stock 64K system). If so desired, switches could be installed with outside accessibility to control these selections.

As part of this upgrade, there are 12 chips that need to be permanently removed from the 1200XL motherboard.

Glue Logic U7, U10, U11, U25

Dynamic RAM U1, U2, U3, U4, U5, U6, U8, U9

Refer to the image below to locate the chips that need removal (they are all socketed). The CO60472 delay line is also not needed, but is often soldered in place, so there's no harm leaving it behind. Although it's rare and could be repurposed.

NOTE: This Memory Expansion will also work on a Modified 1200XL having a 800XL MMU and OS, as well as a BASIC Rom. !!! IMPORTANT !!!  installation of this SRAM board should only be done with the 1200XL motherboard removed from its case and sitting on a solid surface. You gotta press HARD!!!

Top View 1200XL-1mb RAM board

Bottom View 1200XL-1MB Board

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...Atari 1200XL-1MB, Solder-Less 1088K SRAM

Early Prototype shown, although installation is the same for the latest production boards (Click on Image to Enlarge)