git.sur5r.net Git - cc65/blob - libsrc/cbm/cpeekc.s

   1 ;
   2 ; 2016-02-28, Groepaz
   3 ; 2017-06-22, Greg King
   4 ;
   5 ; char cpeekc (void);
   6 ;
   7
   8         .export         _cpeekc
   9
  10 ; Get a system-specific file.
  11 ; Note:  The cbm610, and c128 targets need special
  12 ; versions that handle RAM banking and the 80-column VDC.
  13
  14 .if     .def(__C16__)
  15         .include        "plus4.inc"     ; both C16 and Plus4
  16 .elseif .def(__C64__)
  17         .include        "c64.inc"
  18 .elseif .def(__CBM510__)
  19         .import         CURS_X: zp, SCREEN_PTR: zp
  20         .include        "cbm510.inc"
  21 .elseif .def(__PET__)
  22         .include        "pet.inc"
  23 .elseif .def(__VIC20__)
  24         .include        "vic20.inc"
  25 .endif
  26
  27
  28 _cpeekc:
  29         ldy     CURS_X
  30         lda     (SCREEN_PTR),y  ; get screen code
  31         ldx     #>$0000
  32         and     #<~$80          ; remove reverse bit
  33
  34 ; Convert the screen code into a PetSCII code.
  35 ; $00 - $1F: +$40
  36 ; $20 - $3F
  37 ; $40 - $5f: +$20
  38 ; $60 - $7F: +$40
  39
  40         cmp     #$20
  41         bcs     @sk1            ;(bge)
  42         ora     #$40
  43         rts
  44
  45 @sk1:   cmp     #$40
  46         bcc     @end            ;(blt)
  47         cmp     #$60
  48         bcc     @sk2            ;(blt)
  49         ;sec
  50         adc     #$20 - $01
  51 @sk2:   ;clc                    ; both above cmp and adc clear carry flag
  52         adc     #$20
  53 @end:   rts