There are many decriptions of Atari 130XE upgrades (concerning in majority machines equipped
with 1-bit memory). Some of these computers  have built-in 4-bit memory chips (4464 type -> 64k x 4bit). They have 4 of these chips. I haven't found anywhere description how to expand memory in this case. I present my solution of this problem below.


---> Upgrading your machine to 320kB. <---

Required parts:
 - 4464-type memory chips - 6 pieces
 - 33-Ohm resitors - 3 pieces
 - UCY74LS155 integrated circuit
 - isolated cable - about 1m

Pinouts:

       4464 
    +---+-+---+
/OE |1  +-+ 18| GND 
D0  |2      17| D3
 D1 |3      16| /CAS
/WE |4      15| D2 
/RAS|5      14| A0 
 A6 |6      13| A1
 A5 |7      12| A2 
 A4 |8      11| A3 
VCC |9      10| A7 
    +---------+ 

          UCY74LS155
         +---+-+---+
      1C |1  +-+ 16| VCC
      1G |2     15| 2C 
      DSB|3     14| 2G
      1Y3|4      13|DSA 
      1Y2|5     12| 2Y3
      1Y1|6      11|2Y2 
      1Y0|7      10|2Y1 
      GND|8       9|2Y0 
         +---------+ 

1G,2G - strobe 
DSA,DSB - adres 
1C,2C - data input
1Y0-1Y3,2Y0-2Y3 - data output


Table of states for 74LS155

+---+---+---+---+---+---+---+---+
|DSB|DSA|1G |1C |1Y0|1Y1|1Y2|1Y3|
+---+---+---+---+---+---+---+---+
| X | X | 1 | X | 1 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 1 | 0 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 1 | 0 | 1 | 1 | 1 | 1 | 0 | 1 |
+---+---+---+---+---+---+---+---+
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
+---+---+---+---+---+---+---+---+
| X | X | X | 0 | 1 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+
|DSB|DSA|2G |2C |2Y0|2Y1|2Y2|2Y3|
+---+---+---+---+---+---+---+---+
| X | X | 1 | X | 1 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 |
+---+---+---+---+---+---+---+---+
| 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 |
+---+---+---+---+---+---+---+---+
| 1 | 1 | 1 | 0 | 1 | 1 | 1 | 0 |
+---+---+---+---+---+---+---+---+
| X | X | X | 1 | 1 | 1 | 1 | 1 |
+---+---+---+---+---+---+---+---+


What to do:

1) Desolder one end of R=33-Ohm resistor leading from the CO25953-chip to CAS of extended memory. It's the resistor placed closer to CO25953. In this place solder a bit of cable which next will be connected to 74LS155. Make sure this resistor is connected with extended CAS. For your information: these are 2 pieces of memory chips places closer to front side of computer.


2) Solder 74LS155 on CO25953 (bend off all the pins except 8 and 16 on 74LS155). Marks on both chips should be on one side.


3) Desoldered end of R=33 resistor solder back to one pin (2Y0,2Y1,2Y2 or 2Y3) of 74LS155. For the best result solder it to 2Y2 (11 pin), because it's placed exactly opposite to desoldered end of resistor.


4) Bend off CAS pins (pins no. 16) on the 4464s and solder them pin to pin onto the chip already on the board. ATTENTION: when expanding to 320k, first solder 4 4464s on the already existing chips, and then add 2 more 4464s.


5) Connect DSB DSA address inputs (3 and 13 pin of 74LS155) to the 15 and 16 pin of PIA (6520 or 6521) using long cables. Pin 3 of 74LS155 connect to z16 (Vcc).


6) Data input 2C (15 pin of 74LS155) connect to GND (8 pin).


7) Free (after operation from first point) extendedCAS pinout of CO25953 connect by a cable with 2G input of 74LS155 (14 pin).


8) Folded down 16 pins (/CAS) of extended memory chips connect in pairs (every two from the same layer) and through 3 R=33-Ohm resistors connect wit 3 usused 2Y0-2Y3 pinouts (pins from 9 to 12). One of them is already connected to the resistor from third operation.


After checking the assembly turn on the computer and test the memory.


For the analysis of 74LS155 the state table of it will be helpful.


Note: 4464 chips aren't active when the CAS-es are connected to +5V.