Combat demo: DrawScrollInNMI

       Name: DrawScrollInNMI                                         [Show more]
       Type: Subroutine
   Category: Combat demo
    Summary: Configure the NMI handler to draw the scroll text screen
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ShowScrollText calls DrawScrollInNMI


.DrawScrollInNMI

 JSR WaitForPPUToFinish ; Wait until both bitplanes of the screen have been
                        ; sent to the PPU, so the screen is fully updated and
                        ; there is no more data waiting to be sent to the PPU

 LDA #254               ; Tell the NMI handler to send data up to pattern 254,
 STA firstFreePattern   ; so all the patterns get updated

 LDA #%11001000         ; Set both bitplane flags as follows:
 STA bitplaneFlags      ;
 STA bitplaneFlags+1    ;   * Bit 2 clear = send tiles up to configured numbers
                        ;   * Bit 3 set   = clear buffers after sending data
                        ;   * Bit 4 clear = we've not started sending data yet
                        ;   * Bit 5 clear = we have not yet sent all the data
                        ;   * Bit 6 set   = send both pattern and nametable data
                        ;   * Bit 7 set   = send data to the PPU
                        ;
                        ; Bits 0 and 1 are ignored and are always clear
                        ;
                        ; The NMI handler will now start sending data to the PPU
                        ; according to the above configuration, splitting the
                        ; process across multiple VBlanks if necessary

 RTS                    ; Return from the subroutine