Back to Table of Contents 4.11 LOGIC BOARD IC CHIP FUNCTIONS (Locations refer to the 2-port version, these may be different on the 4-port model.) A1 4050 Video signal buffer A2 C014806 CPU 6502C This is a custom version of the standard 6502 microprocessor. It is functionally identical to a standard 6502, except that hardware has been added to it that allows the ANTIC chip to do Direct Memory Access (DMA). A3 C012296 ANTIC This chip is a microprocessor that reads data directly from RAM to determine how the screen should be drawn and controls the GTIA to actually generate the graphics. The ANTIC is also responsible for processing NMI's. A5 C014805 GTIA This chip is responsible for generating the video signal to the TV, generating sprites, reading the joystick trigger buttons, and controlling the reading of the joysticks and keypads (the actual reading is done by POKEY). A6 74LS139 Address decoding. A7 C012294 POKEY This chip is responsible for generating sound, reading the position of the joystick, reading the keypad buttons, processing IRQ's and, controlling the serial I/O port which is accessible through the expansion connector. A8 C019156A ROM BIOS This is a 2K ROM chip that holds the character set and the BIOS software. The BIOS initializes the system and to service interrupts. A9,10,11 4052 Keypad scanning multiplexers. A14 74LS125 Control signal buffering. A15 74LS51 DRAM control signals. A16,17 74LS258 DRAM address multiplexers. A18-25 MK4516 1x16K DRAM A26 4013 Power on/off switch latch. A27 74LS00 Miscellaneous logic. Back to Table of Contents