Skip to navigation

⌂ ∞ Elite on the BBC Micro and NES

Equipment: MoveEquipmentDown

[NES version, Bank 0]

       Name: MoveEquipmentDown                                       [Show more]
       Type: Subroutine
   Category: Equipment
    Summary: Move the currently selected item down the list of equipment

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * EQSHP calls MoveEquipmentDown




.MoveEquipmentDown

 JSR PrintEquipment     ; Print the name and price for the equipment item in
                        ; XX13

 LDA XX13               ; Set A = XX13 + 1, so A contains the item number below
 CLC                    ; the currently selected item in the equipment list
 ADC #1

 CMP Q                  ; If A has not reached Q, which contains the number of
 BNE eqdn1              ; items in the list plus 1, then we have not fallen off
                        ; the bottom of the list, so jump to eqdn1 to skip the
                        ; following

 LDA Q                  ; Set A = Q - 1 to set the currently selected item to
 SBC #1                 ; the bottom item in the list, so we don't go past the
                        ; bottom of the list (the subtraction works because we
                        ; just passed through a BNE, so the comparison was
                        ; equal which sets the C flag)

.eqdn1

 STA XX13               ; Store the new item number in XX13, so we move down the
                        ; equipment list

 JMP UpdateEquipment    ; Jump up to UpdateEquipment to highlight the newly
                        ; chosen item of equipment, update the Cobra Mk III,
                        ; redraw the screen and rejoin the main EQSHP routine to
                        ; continue checking for button presses