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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: CLYNS

[Elite-A, Parasite]

       Name: CLYNS                                                   [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Clear the bottom three text rows of the mode 4 screen by sending a
             clr_line command to the I/O processor

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * cour_buy calls CLYNS
             * EQSHP calls CLYNS
             * hm calls CLYNS
             * JMTB calls CLYNS
             * menu calls CLYNS
             * n_buyship calls CLYNS
             * qv calls CLYNS
             * TITLE calls CLYNS
             * TT102 calls CLYNS
             * TT219 calls CLYNS




 Returns:

   A                    A is set to 0

   Y                    Y is set to 0



.CLYNS

 LDA #%11111111         \ Set DTW2 = %11111111 to denote that we are not
 STA DTW2               \ currently printing a word

 LDA #20                \ Move the text cursor to row 20, near the bottom of
 STA YC                 \ the screen

 JSR TT67               \ Print a newline, which will move the text cursor down
                        \ a line (to row 21) and back to column 1

 LDY #1                 \ Move the text cursor to column 1
 STY XC

 DEY                    \ Set Y = 0, so the subroutine returns with this value

 LDA #&84               \ Send command &84 to the I/O processor:
 JMP tube_write         \
                        \   clr_line()
                        \
                        \ which will clear the bottom three text rows of the top
                        \ part of the screen and return from the subroutine
                        \ using a tail call