mirror of
https://github.com/RevCurtisP/C02.git
synced 2024-11-28 10:51:14 +00:00
38 lines
1.5 KiB
Plaintext
38 lines
1.5 KiB
Plaintext
;C02 VCS Library - Assembly Language Subroutines
|
|
|
|
;addbcd(addend, &varble) - Add Number to BCD variable
|
|
;adcbcd(addend, &varble) - Add Number w/Carry to BCD variable
|
|
;Args: A = Number to Add
|
|
; X,Y = Pointer to Variable to Add To
|
|
;Sets: TEMP0,TEMP1 = Pointer to Color Table
|
|
;Affects: A,Y,C,N,Z
|
|
;Updates: Variable Pointed to by X,Y
|
|
;Returns: A = Result of Addition
|
|
ADDBCD: CLC ;Clear Carry - Regular Add
|
|
ADCBCD: STX TEMP0 ;Save Pointer to Variable
|
|
STY TEMP1
|
|
LDY #0
|
|
SED ;Set Decimal Mode
|
|
ADC (TEMP0),Y ;Add Accumulator to Variable
|
|
STA (TEMP0),Y ;Store Result in Variable
|
|
CLD ;Clear Decimal Mode
|
|
RTS ;Return
|
|
|
|
;posobj(hrzpos, object) - Position Object
|
|
;Args: A = Horizontal Position
|
|
; Y = Object (0=Player0, 1=Player1, 2=Missile0, 3=Missle1, 4=Ball)
|
|
;Affects: A,C,Z
|
|
POSOBJ: SEC
|
|
STA WSYNC ;Wait for Beginning of Scanline
|
|
POSOBL: SBC #15 ;2 2 - each time thru this loop takes 5 cycles, which is
|
|
BCS POSOBL ;2 4 - the same amount of time it takes to draw 15 pixels
|
|
EOR #7 ;2 6 - The EOR & ASL statements convert the remainder
|
|
ASL ;2 8 - of position/15 to the value needed to fine tune
|
|
ASL ;2 10 - the X position
|
|
ASL ;2 12
|
|
ASL ;2 14
|
|
STA.WY HMP0,Y ;5 19 - store fine tuning of X
|
|
STA RESP0,Y ;4 23 - set coarse X position of object
|
|
RTS ;6 29
|
|
|