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⌂ ∞ ▽ Elite on the 6502

Utility routines: SETL1

[Commodore 64 version]

       Name: SETL1                                                   [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: Set the 6510 input/output port register to control the memory map

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * COLD calls SETL1
             * DKSANYKEY calls SETL1
             * KERNALSETUP calls SETL1
             * LOD calls SETL1
             * Main flight loop (Part 15 of 16) calls SETL1
             * MVTRIBS calls SETL1
             * NOSPRITES calls SETL1
             * PTCLS2 calls SETL1
             * RDKEY calls SETL1
             * SIGHT calls SETL1
             * startbd calls SETL1
             * stopbd calls SETL1
             * SVE calls SETL1




 See page 260 of the Programmer's Reference Guide for details on how the 6510
 input/output port register works.



 Arguments:

   A                    The new value of the input/output port register:

                          * Bit 0 controls LORAM

                          * Bit 1 controls HIRAM

                          * Bit 2 controls CHAREN



.SETL1

 SEI                    ; Disable interrupts while we set the 6510 input/output
                        ; port register

 STA L1M                ; Store the new value of the port register in L1M

 LDA l1                 ; Set bits 0 to 2 of the port register at location l1
 AND #%11111000         ; ($0001) to bits 0 to 2 of L1M, leaving bits 3 to 7
 ORA L1M                ; unchanged
 STA l1                 ;
                        ; This sets LORAM, HIRAM and CHAREN to the new values

 CLI                    ; Re-enable interrupts

 RTS                    ; Return from the subroutine