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⌂ ∞ ▽ Elite on the 6502

Version analysis of NLIN2

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

       Name: NLIN2
       Type: Subroutine
   Category: Drawing lines
    Summary: Draw a screen-wide horizontal line at the pixel row in A



 This draws a line from (2, A) to (254, A), which is almost screen-wide and
 fits in nicely between the border boxes without clashing with it.



 Arguments:

   A                    The pixel row on which to draw the horizontal line



.NLIN2

 STA Y1                 \ Set Y1 = A

Code variation 1 of 4Related to Elite's use of the Tube

This variation is blank in the Cassette, Disc (flight), Disc (docked), Master and Electron versions.

6502SP
 STA Y2                 \ Set Y2 = A

Code variation 2 of 4Related to the screen mode

This variation is blank in the Cassette, Disc (flight), Disc (docked) and Electron versions.

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
 LDA #YELLOW            \ Switch to colour 1, which is yellow
 STA COL

 LDA #YELLOW            \ Send a #SETCOL YELLOW command to the I/O processor to
 JSR DOCOL              \ switch to colour 1, which is yellow

 LDX #2                 \ Set X1 = 2, so (X1, Y1) = (2, A)
 STX X1

 LDX #254               \ Set X2 = 254, so (X2, Y2) = (254, A)
 STX X2

Code variation 3 of 4Related to Elite's use of the Tube

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked
Master
6502SP
Electron
 BNE HLOIN              \ Call HLOIN to draw a horizontal line from (2, A) to
                        \ (254, A) and return from the subroutine (this BNE is
                        \ effectively a JMP as A will never be zero)

 JSR HLOIN3             \ Call HLOIN3 to draw a line from (2, A) to (254, A)

 JSR LL30               \ Call LL30 to draw a line from (2, A) to (254, A)

                        \ Fall through into HLOIN to draw a horizontal line from
                        \ (2, A) to (254, A) and return from the subroutine

Code variation 4 of 4Related to the screen mode

This variation is blank in the Cassette, Disc (flight), Disc (docked) and Electron versions.

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
 LDA #CYAN              \ Switch to colour 3, which is cyan or white
 STA COL

 RTS                    \ Return from the subroutine

 LDA #CYAN              \ Send a #SETCOL CYAN command to the I/O processor to
 JMP DOCOL              \ switch to colour 3, which is cyan or white