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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: SUBTRACT_CYCLES

[NES version, Common]

       Name: SUBTRACT_CYCLES                                         [Show more]
       Type: Macro
   Category: Drawing the screen
    Summary: Subtract a specified number from the cycle count
  Deep dive: Drawing vector graphics using NES tiles

    Context: See this macro in context in the source code
 References: This macro is used as follows:
             * ClearBuffers uses SUBTRACT_CYCLES
             * ClearMemory uses SUBTRACT_CYCLES
             * ClearPlaneBuffers (Part 1 of 2) uses SUBTRACT_CYCLES
             * ClearPlaneBuffers (Part 2 of 2) uses SUBTRACT_CYCLES
             * ConsiderSendTiles uses SUBTRACT_CYCLES
             * SendBarNamesToPPU uses SUBTRACT_CYCLES
             * SendBarPatts2ToPPU uses SUBTRACT_CYCLES
             * SendBarPattsToPPU uses SUBTRACT_CYCLES
             * SendBuffersToPPU (Part 2 of 3) uses SUBTRACT_CYCLES
             * SendBuffersToPPU (Part 3 of 3) uses SUBTRACT_CYCLES
             * SendNametableToPPU uses SUBTRACT_CYCLES
             * SendOtherBitplane uses SUBTRACT_CYCLES
             * SendPalettesToPPU uses SUBTRACT_CYCLES
             * SendPatternsToPPU (Part 1 of 6) uses SUBTRACT_CYCLES
             * SendPatternsToPPU (Part 3 of 6) uses SUBTRACT_CYCLES
             * SendPatternsToPPU (Part 5 of 6) uses SUBTRACT_CYCLES




 The following macro is used to subtract cycles from the cycle count:

   SUBTRACT_CYCLES cycles

 The cycle count is stored in the variable cycleCount.



 Arguments:

   cycles               The number of cycles to subtract from the cycle count



MACRO SUBTRACT_CYCLES cycles

 SEC                    ; Subtract cycles from cycleCount(1 0)
 LDA cycleCount
 SBC #LO(cycles)
 STA cycleCount
 LDA cycleCount+1
 SBC #HI(cycles)
 STA cycleCount+1

ENDMACRO