changing color registers or Player/Missile positions. Mode 1 Instruction - Jump When Mode value is 1 ANTIC executes a Jump in its program (the Display List). The next two bytes in the Display List are loaded into ANTIC registers DLISTL/DLISTH ($D402-$D403hex/54274-54275dec) changing the execution point of the next instruction. There are two kinds of Jumps: 01hex/1dec JMP - Jump to address. This is used to load a new execution address in the middle of Display List execution, typically when the Display List must cross over a 1K boundary. 41hex/65dec JVB - Jump to address and wait for Vertical Blank. (JMP + LMS bit set) This is used to end the Display List. The address used should be the starting address of the Display List. The DLIST registers are also updated by the Operating System's Vertical Blank Interrupt (VBI) routine using the values in shadow registers SDLSTL/SDLSTH (0230-0231hex/560-561dec). When the OS VBI routine is enabled direct updates to the ANTIC DLIST registers by the CPU or the ANTIC Jump instructions will be overwritten by the OS during the next Vertical Blank. This implies that an ANTIC JVB (Jump and wait for Vertical Blank) instruction that specifies an invalid address (or a valid address that differs from the shadow SDLST value) has no real effect on the display. The JVB's argument usually points to the beginning of the same Display List, but it can also point to another Display List, so that a chain of Display Lists is executed after consecutive vertical blanks. Of course, to give ANTIC control over the start of the next Display List the OS Vertical Blank interrupt must be disabled to prevent it overwriting ANTIC hardware registers with the shadow register values. Modes 2 to F Instructions - Playfield Character and Map Modes The following is the list of ANTIC graphics mode instructions. For more detailed descriptions of each Mode see the Playfield Graphics Modes section. The memory requirement for a Mode Line is determined by two factors: The width bits set in the DMACTL hardware register. The presence of the Horizontal Fine Scroll Display List Instruction Modifier. The Horizontal Fine Scroll Modifier will change the memory requirement for the current Mode Line from the DMACTL-specified width to the next largest value. Instruction Modifiers Bits 7:4 are modifiers for Playfield Mode instructions in bits 3:0. Playfield Mode Instruction values range from $02 to $0F. Modifier bit value