By John Hardie

Based upon the 65XE/320K Upgrade
by: Scott Peterson

  • The Atari 1450XLD was originally designed to be the flagship of the Atari XL line of home computers. Unfortunately, it was never publically released for sale. Its original configuration called for:
      - 64K Ram
      - Internal DS/DD Disk Drive
      - Internal 300 Baud Modem
      - Internal Speech Synthesizer
      - 1200XL style Keyboard w/ LED's and Function Keys F1-F4
      - Parallel Bus Interface for the 1090XL Expansion System
  • Internally, the circuitry of the 1450XLD is very similar to the XE series of computers in that it contains the FREDDIE chip used in the XE's for Ram access. Few modifications to Scott Peterson's original 65XE/320K upgrade were necessary to get it to work on the 1450XLD. Before we get down to business, let's get the usual disclaimer out of the way.

  • DISCLAIMER: Installation of this upgrade is done at your own risk. I guarantee the information that follows to be technically correct to the best of my knowledge.

  • On with the good stuff... To perform this upgrade you will need the following tools:

    - Low wattage soldering iron (15-25 watt)
    - #2 Philips head screwdriver
    - Small Flat-blade screwdriver
    - Fine tip needle-nose pliers

  • The chips on the 1450XLD motherboard should be socketed, so there should be no need for any de-soldering.

    Parts and Supplies:

    - Z1 74LS158
    - Z2 CO25953 (Atari Custom Chip, Best Electronics)
    - Z3-Z10 256K Dram (150ns) [41256]
    - R1-R3 33 ohm resistors
    - XZ1-XZ10 (10) 16-pin sockets
    - 30 gauge wire (Radio Shack #278-501)
    - Electrical tape

  • First, remove all the 64K Ram chips from their sockets. Solder a 16-pin socket to the top of each Ram chip.

  • Take one of the two remaining sockets and bend up all of the pins except 8 and 16. Now solder this socket to the top of U21 (74LS138). Replace U21 into the 1450XLD.

  • Take the last 16-pin socket and bend up pins 1, 2, 3, 4, and 15. Clip off pins 5, 6, 7, 9, 10, 11, 12, 13, and 14. Solder this socket to the top of U46 (74LS123). Replace U46 into the 1450XLD.

  • Remove U25 (FREDDIE - CO61922 or CO61991) and bend up pins 23, 24, and 35. Replace U25 in its socket.

  • Remove the motherboard. On the bottom of the motherboard, jumper together all pin one's of each 64K Ram chip socket. For the remainder of the upgrade, be extra careful that the pins that were bent up are straight and not touching anything and that you don't accidentally short any pins/wires or what-not together.

  • When cutting the jumper wire, strip back the minimum amount of insulation necessary to tin the wire and make contact. Also, measure the wire so that it is not stretched tight between connections. There should be excess insulated wire so that it is loose when it is soldered to the pins of the sockets. It should not strain, pull, or bend any pins on any sockets or chips.

  • On each 256K Ram chip bend up pin 15 and plug it into the sockets which you soldered to the tops of the 64K Ram chips. Jumper the pin 15's of each 256K Ram chip together using the wire.

  • Prepare three jumper wires by measuring the correct lengths needed for the first 3 connections listed below, cutting them in half, and soldering each half to one end of one of the 33 ohm resistors. Your jumper wires should look like this:
                    ^        ^        ^
                  wire   resistor   wire
  • Wrap the resistor connections in electrical tape.

  • Let's call the socket soldered to U46 (74LS123) - XZ1 and the socket soldered to U21 (74LS138) - XZ2. Connect the resistorized jumpers accordingly:
         XZ1 pin 4    -R1-    U45 pin 1 (bottom of board)
         XZ2 pin 11   -R2-    U45 pin 15 (bottom of board)
         XZ2 pin 10   -R3-    Any 256K Ram chip pin 15
  • Connect these remaining jumper wires:
         XZ1 pin 15   -   XZ1 pin 8
         XZ1 pin 1    -   U26 pin 30 (CO14805)
         XZ1 pin 2    -   U2 pin 15 (6520)
         XZ1 pin 3    -   U2 pin 16
         XZ2 pin 3    -   U2 pin 12
         XZ2 pin 4    -   U2 pin 13
         XZ2 pin 5    -   U2 pin 14
         XZ2 pin 9    -   U17 pin 9 (CO12296 or CO21697)
         XZ2 pin 1    -   U18 pin 17 (74LS244)
         XZ2 pin 2    -   U18 pin 2
         XZ2 pin 6    -   U25 pin 35 (CO61922 or CO61991)
         XZ2 pin 12   -   U25 pin 23
         XZ2 pin 13   -   U25 pin 24
         XZ2 pin 15   -   U25 pin 5
         XZ2 pin 14   -   XZ2 pin 16
         XZ2 pin 7    -   XZ2 pin 8
  • Plug the 74LS158 into XZ1 and the CO25953 into XZ2.

  • This completes the memory upgrade. This upgrade can easily be reversed by simply unplugging the 74LS158 from XZ1 and the CO25953 from XZ2 and plugging back in pins 23, 24, and 35 of U25.

  • A few last notes... The upgrade is a tight fit. The modem card can be slipped off during installation and put back on when you're finished. To get the keyboard to rest evenly on the case it might be necessary to clip the plastic screw support under the front right-hand corner of the motherboard with wire cutters.

  • Any software compatible with Scott Peterson's 65XE/320K upgrade should work fine here also, although we haven't done a lot of software testing at this point other than with SpartaDos 3.2D.

  • This upgrade has NOT been tested on a 1450XLD TONG motherboard. It should still work but I make no guarantees.

  • Best Electronics is the BEST supplier of Atari parts around. Give Brad a call at 1-408-243-6950.

  • If you have any problems with this upgrade or have any questions or information concerning the 1450XLD, please feel free to contact me.
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