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68 lines
2.3 KiB
Plaintext
68 lines
2.3 KiB
Plaintext
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; Vera Layer Control Assembly Language Routines for C02
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; Requires External Routines GETMEA, GETMBX, GETTBS,
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; and External Variables TEMP0,TEMP1,TEMP2
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;getvca(layer, index) - Get Vera Character Address
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;Args: A = Layer (0/1)
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; Y = Character Index
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;Sets: TEMP0 = Bank
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; TEMP1 = Address LSB
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; TEMP2 = Address MSB
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;Returns: A = Bank
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; Y = Address LSB
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; X = Address MSB
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GETVCA: PHA ;Save Layer Number
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STY TEMP1 ;Set Offset LSB to Index
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LDA #0 ;Set Offset MSB to Zero
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ASL TEMP1 ;Multiple Offset by 2
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ROL
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STA TEMP2 ;and Store MSB
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PLA ;Restore Layer Number
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JSR GETTBS ;Get Tile Base
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TXA ;Add Tile Base LSB
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CLC
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ADC TEMP1 ;to Offset LSB
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STA TEMP1
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TYA ;Add Tile Base MSB
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ADC TEMP2 ;to Offset MSB
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STA TEMP2
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LDA #0 ;Set Bank
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ADC #0 ;to Carry
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STA TEMP0
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LDX #2 ;Set Count to 2
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JMP ASLADR ;and Shift Address Left
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;getvcd(layer, index) - Read Vera Character Data to Array
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;Args: A = Layer (0/1)
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; Y = Character Index
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;Uses: DSTLO,DSTHI = Address of Array
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;Destroys: TEMP0,TEMP1,TEMP2
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;Returns: A = Number of Bytes Read
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GETVCD: JSR SETVAC ;Set Vera Address to Character Address
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LDA #8 ;Set Byte Count to 8
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JMP GETMEA ;and Read Bytes into Array
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;setvac(layer, index) - Set Vera Address to Character Address
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;Args: A = Layer (0/1)
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; Y = Character Index
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;Sets: TEMP0 = Bank
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; TEMP1 = Address LSB
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; TEMP2 = Address MSB
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;Returns: A = Bank + Auto-Increment
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; Y = Address LSB
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; X = Address MSB
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SETVAC: JSR GETVCA
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ORA #$10 ;Set Auto-Increment to 1
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JMP SETADR ;and Set Vera Address
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;setvcd(layer, index) - Write Vera Character Data from Array
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;Args: A = Layer (0/1)
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; Y = Character Index
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;Uses: SRCLO,SRCHI = Address of Array
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;Destroys: TEMP0,TEMP1,TEMP2
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;Returns: A = Number of Bytes Read
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GETVCD: JSR SETVAC ;Set Vera Address to Character Address
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LDA #8 ;Set Byte Count to 8
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JMP SETMEA ;and Read Bytes into Array
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