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Atari 8bit Technical Documentation
Documentation Technique Atari 8bit


The Atari Vectors
The Atari Vectors

A vector is the address of an address, and this address has the vector name. That means that vector is a memory pointer which points towards 2 successive bytes, 2 bytes which represent and code an address.

For example, when a reset of the 6502 processor occurs, the 16 bit (16 bits = 2 bytes) PC register of the 6502 (PC = Program Counter) loads the RESET vector which is located at the address $FFFC-$FFFD.

$FFFC normally contains the byte $AA, and $FFFD normally contains the byte $C2 for Atari XL/XE. The RESET vector thus contains the address $C2AA. The code at $C2AA is run when 6502 processor of the Atari computer receives a reset order (hardware signal).

The RESET vector (addresses $$FFFC-$FFFD) contains the address $C2AA.

Other important vectors:

ADDRESS: $0002-$0003 $000A-$000B $000C-$000D

The brackets notation in the Atari assembler, as in expression JSR (DOSVEC), indicates that the address contained in the DOSVEC vector must be used by instruction JSR. If the DOSVEC vector contains $0700, then the code to execute will be JSR $0700.


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