SHARE |
|
![]() ![]() |
by Bill Degnan - 05/16/2022 11:38 |
![]() Atari 400 homebrew RAM expansion front. Click image for larger view.
Unlike modern RAM upgrades, this one is an actual vintage wire-wrapped 48K upgrade constructed in 1981 or so. ![]() Atari 400 homebrew RAM expansion obverse. Note the wirewrap connections and pin 4 has been cut. Click image for larger view.
![]() The wire jumpers added to the motherboard to allow for the RAM expansion to be made available to the system. Click image for larger view.
![]() Here is the RAM expansion as it would appear installed within the Faraday cage (removed) within the Atair 400. Click image for larger view.
![]() So how much RAM is available? Click image for larger view.
When I test the RAM in basic using the command ?FRE(0) the system reports 29690. In theory this RAM card has chips enough for 64K. I tracked down the original notes and schematic for this RAM daughterboard to see what was going on. Apparently the board was originally wired for 48K. In 1984 pin 4 was cut to step down the board to supply RAM from 00-32K only. With the advent of the 16K game cartridge (such as Pole Position) RAM space 32K-48K was needed for the larger carts. Essentially without a switch (electronic or software) RAM expansion for a 400 maxes out at 32K, if you want to use 16K carts. Download schematic and hand-written project notes and view photos This particular Atari 400 was owned by Roy Brader. He won the computer prize drawing held by Avantec. Reply |