ATARI 1450XLD MEMORY UPGRADE
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
- 64K Ram
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.
- 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
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) 
- 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
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
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
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
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.