Version analysis of me1 - Elite on the 6502

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

Cassette, Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron

Code variations between these versions are shown below.

       Name: me1
       Type: Subroutine
   Category: Flight
    Summary: Erase an old in-flight message and display a new one


 Arguments:

   A                    The text token to be printed

   X                    Must be set to 0


.me1

 STX DLY                \ Set the message delay in DLY to 0, so any new
                        \ in-flight messages will be shown instantly

 PHA                    \ Store the new message token we want to print

Code variation 1 of 2Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Electron versions.

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

 LDA MCH                \ Set A to the token number of the message that is
 JSR mes9               \ currently on-screen, and call mes9 to print it (which
                        \ will remove it from the screen, as printing is done
                        \ using EOR logic)

 PLA                    \ Restore the new message token

Code variation 2 of 2Specific to an individual platform

This variation is blank in the Disc (docked), 6502 Second Processor and Master versions.

Cassette, Flight, Electron
 EQUB &2C               \ Fall through into ou2 to print the new message, but
                        \ skip the first instruction by turning it into
                        \ &2C &A9 &6C, or BIT &6CA9, which does nothing apart
                        \ from affect the flags