$FD50/64848:   Initialise System Constants

Jump from $FCF5, $FF87:

FD50: A9 00     LDA #$00
FD52: A8        TAY

Jump from $FD5D:

FD53: 99 02 00  STA $0002,Y   ; Unused
FD56: 99 00 02  STA $0200,Y   ; BASIC Input Buffer (Input Line from Screen)
FD59: 99 00 03  STA $0300,Y   ; Vector: BASIC Error Message
FD5C: C8        INY
FD5D: D0 F4     BNE $FD53
FD5F: A2 3C     LDX #$3C
FD61: A0 03     LDY #$03
FD63: 86 B2     STX $B2       ; Pointer: Start Address of Tape Buffer
FD65: 84 B3     STY $B3       ; Pointer: Start Address of Tape Buffer
FD67: A8        TAY
FD68: A9 03     LDA #$03
FD6A: 85 C2     STA $C2       ; Start Address for LOAD and Cassette Write

Jump from $FD86:

FD6C: E6 C2     INC $C2       ; Start Address for LOAD and Cassette Write

Jump from $FD84:

FD6E: B1 C1     LDA ($C1),Y   ; Start Address for LOAD and Cassette Write
FD70: AA        TAX
FD71: A9 55     LDA #$55
FD73: 91 C1     STA ($C1),Y   ; Start Address for LOAD and Cassette Write
FD75: D1 C1     CMP ($C1),Y   ; Start Address for LOAD and Cassette Write
FD77: D0 0F     BNE $FD88
FD79: 2A        ROL
FD7A: 91 C1     STA ($C1),Y   ; Start Address for LOAD and Cassette Write
FD7C: D1 C1     CMP ($C1),Y   ; Start Address for LOAD and Cassette Write
FD7E: D0 08     BNE $FD88
FD80: 8A        TXA
FD81: 91 C1     STA ($C1),Y   ; Start Address for LOAD and Cassette Write
FD83: C8        INY
FD84: D0 E8     BNE $FD6E
FD86: F0 E4     BEQ $FD6C

Jump from $FD77, $FD7E:

FD88: 98        TYA
FD89: AA        TAX
FD8A: A4 C2     LDY $C2       ; Start Address for LOAD and Cassette Write
FD8C: 18        CLC
FD8D: 20 2D FE  JSR $FE2D     ; Read / Set Top of Memory
FD90: A9 08     LDA #$08
FD92: 8D 82 02  STA $0282     ; Pointer: Bottom of Memory for Operating System
FD95: A9 04     LDA #$04
FD97: 8D 88 02  STA $0288     ; High Byte of Screen Memory Address
FD9A: 60        RTS

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Kernal-Reference:

 LDA $FD93,X : $FCBD

 LDA $FD94,X : $FCC3