Back to Table of Contents 4.12 DIFFERENCES BETWEEN THE 5200 AND ATARI 8-BIT COMPUTERS The 5200 is basically an Atari Computer without a keyboard. It has all the major chips that the computers have with the exception of the PIA chip, but most of the chips are at different memory locations. The differences between the two machines are as follows: * Memory The 5200 has a fixed 16K of RAM. Memory locations $00-$18 and $200-$21B are reserved for the BIOS to use. * ROM The BIOS ROM of the 5200 is only 2K instead of 10K. Virtually none of the computer's BIOS functions are implemented on the 5200. * ANTIC The 5200 does not have a System Reset key, so bit 5 of NMIST is not used. * GTIA The trigger inputs, TRIG0-TRIG3 are connected to the bottom buttons of the controllers. The 5200 does not have Start, Select, or Option buttons, so these lines are used as outputs. Bit 2 of CONSOL enables and disables the joystick pots. Bits 0 and 1 control which keypad controller is being read. This only affects the keypad buttons, and the top trigger buttons. * POKEY The eight paddle inputs from the computer are now wired to the joysticks, 2 to each stick, one for vertical position and the other for horizontal position. The joysticks are read in the same way that the computer's paddles are read. On the 5200 the KBCODE register bits 1-4 hold the scan code from the currently selected keypad controller. Bit 6 of KBCODE is used to read the top button of the controllers instead of the SHIFT key. They also cause the BREAK-key interrupt. The POKEY's serial lines are connected to the expansion connector. * Cartridge The cartridges can be up to 32K. There are two interlock connectors that are wired together on a cartridge board. The 5200 uses this as a switch for the cartridge's power connections and as a Reset signal. Therefore, a cartridge may be safely removed or inserted while the 5200 is powered on. Back to Table of Contents