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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: SEND_DATA_TO_PPU

[NES version, Common]

       Name: SEND_DATA_TO_PPU                                        [Show more]
       Type: Macro
   Category: Drawing the screen
    Summary: Send a specified block of memory to the PPU
  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:
             * SendNametableToPPU uses SEND_DATA_TO_PPU
             * SendPatternsToPPU (Part 3 of 6) uses SEND_DATA_TO_PPU
             * SendPatternsToPPU (Part 5 of 6) uses SEND_DATA_TO_PPU




 The following macro is used to send bytes to the PPU:

   SEND_DATA_TO_PPU byte_count

 It sends a block of byte_count bytes from memory to the PPU, starting with the
 Y-th byte of the data block at address dataForPPU(1 0). It also updates the
 index in Y to point to the byte after the block that is sent.



 Arguments:

   byte_count           The number of bytes to send to the PPU

   Y                    The index into dataForPPU(1 0) from which to start
                        sending data



 Returns:

   Y                    The index in Y is updated to point to the byte after the
                        block that is sent



MACRO SEND_DATA_TO_PPU byte_count

 FOR I%, 1, byte_count

  LDA (dataForPPU),Y    ; Send the Y-th byte of dataForPPU(1 0) to the PPU
  STA PPU_DATA

  INY                   ; Increment the index in Y

                        ; Repeat the above code so that we run it byte_count
                        ; times, so we send a total of byte_count bytes from
                        ; memory to the PPU

 NEXT

ENDMACRO