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Old news? Memory cards retro information


EKMELSOFT
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I was reading last week an old review of the TI99/4a computer from January 1983. The article explained -- the TI is 16 bit so it can access 64k memory expansion no problem. Texas Instruments marketed the 32K mem cards for memory chips cost a lot more back then. The author of the review was saying TI intended for you buy two 32K cards for full 64K expansion. I never heard this before and i never have stuck two 32k cards in a PEB for I thought the software would not address it. Anyone heard of this idea from anyplace ? Was the reviewer wrongly informed or did TI plan on something like this but dropped it? Just throwing out there for discussion.

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Yeah do not put two 32k cards in the 4/a..

 

The memory map is so:

Address space

>0000 ------------------+
      | Console ROM     |
      +                 +
      |                 |            +------------------+ >8000
>2000 +-----------------+            | (mirror of RAM)  |
      | Low memory      |           /|                  |
      +                 +          / |>8300-83FF: RAM   |
      | expansion       |         /  +------------------+ >8400
>4000 +-----------------+        /   |>8400: sound chip |
      | Peripheral      |       /    |       write      |
      + cards ROM       +      /     |                  |
      |                 |     /      +------------------+ >8800
>6000 +-----------------+    /       |>8800: VDP read   |
      | Cartridge       |   /        |>8802: VDP status |
      + ROM/RAM         +  /         |                  |
      |                 | /          |>8C00: VDP write  |
>8000 +-----------------+-           |>8C02: set address|
      | scratch-pad RAM |            |                  |
      + memory-mapped   +            |                  |
      | devices         |            +------------------+ >9000
>A000 +-----------------+-           |>9000: speech     |
      | High memory     | \          | synthesizer read | 
      + expansion       +  \         |                  |
      |                 |   \        |>9400: speech     |
>C000 +                 +    \       | synthesizer write|
      |                 |     \      +------------------+ >9800
      +                 +      \     |>9800: GROM read  |    
      |                 |       \    |>9802: read addr  |
>E000 +                 +        \   |                  |
      |                 |         \  |>9C00: write data |
      +                 +          \ |>9C02: set address|
      |                 |           \|                  |
>FFFF +-----------------+            |                  |
                                     +------------------+ >9FFF

Memory expansion
The 32 Kbytes of slow, 8-bit memory installed in the PE-Box are installed as two distinct domains: 8K at >2000-3FFF known as the "low memory expansion", and 24K at >A000-FFFF, known as the "high memory expansion".
(info stolen from theirry's tech pages)
Greg
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TI did eventually develop a card called the 64K ExtraRAM (I have some of the technical documentation on it) and a 128K SuperRAM. The SuperRAM cards bank switched memory in the normal 32K space, cartridge ROM space, and DSR space. This gave you ready access to a maximum of 48K of memory at once. The ExtraRAM card did similar things.

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But, still, the TMS9900 CPU can directly address only 64KiB of memory—and, the 32KiB expansion RAM, indeed, maxed out the directly-addressable memory. The other 32KiB are 8KiB console ROM, 8KiB DSR ROM, 8KiB cartridge ROM and 8KiB for memory-mapped devices (including 1KiB scratchpad RAM, only 256 bytes of which actually get used)—per @arcadeshopper’s nice text graphic above. Anything more must use a paging scheme that uses pages in existing RAM, such as what @Ksarul’s above post mentions.

 

...lee

Edited by Lee Stewart
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