The following document was submitted by Dennis Armstrong.
Thanks to Frank Lockwood for putting me in touch with Dennis.

The ST RAM

For its ST-compatible memory, the TT motherboard uses dynamic ram chips of a 256Kx4bit size.
Some compatible Part Numbers:

[ Webmaster's note: Jim DeClercq sent me something about upgrading the motherboard to 8 MB ]

ST RAM Daughterboards (2 MB and 8 MB)

ATARI offered two daughterboards to raise the ST memory configuration to 4 MB or 10 MB.

2 MB Board (CA400313-xxx)

Uses the same memory chips as on the motherboard; no configuration headers are required.

2/8 MB Board (CA401059-xxx)

The board contains the following jumpers to select the 2MB or 8MB memory configuration:

jumper2 MB8 MB
W1 1-2 2-3
W2 open 2-3

Location:

       |    |
       |    |     W1   W2
       |    |     3    3
       |    |     2    2
       |    |     1    1
       \----/
        U13
  

The 8 MB version of the board uses dynamic ram chips of a 1Mx4bit size.
Some compatible Part Numbers:

[ Webmaster's note: it is possible to upgrade the 2 MB version to 8 MB, as explained here. ]

ST RAM Addresses

Address Function
Base system 000008 - 000800 System Memory
000800 - 1FFFFF Motherboard (2 MB)

Address Function
4 MB system 1FFFFF - 3FFFFF 2 MB Expansion
800000 - 9FFFFF Motherboard

Address Function
10 MB system 000000 - 7FFFFF 8 MB Expansion
800000 - 9FFFFF Motherboard


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