;-------------------------------
; #JMPB4BB
; boot2 jumps to $B4BB for a
; nibble check
; e.g. Troll's Tale
;-------------------------------
_jmpb4bb
         lda   gIsMaster  ; if DOS 3.3 lomem bootloader
         bne   jmpb4bb_exit
         lda   #$0C
         sta   gDisplayBytes
         ldx   #$84
         ldy   #$03
         jsr   compare    ; and T00,S0C,$84 ==
         !byte $4C,$BB,$B4
         bcs   jmpb4bb_exit
         lda   #s_jmpb4bb
         lda   #$0C
         ldx   #$84
         ldy   #$03
         jsr   modify     ; then set T00,S0C,$84 =
         !byte $AD,$E9,$37
;
; also check a variant that redirects the DOS input
; vector through code that is only loaded by the
; protection check we just bypassed
;
         lda   #$0D
         ldx   #$BA
         ldy   #$03
         jsr   compare    ; if T00,S0D,$BA ==
         !byte $4C,$0B,$37
         bcs   jmpb4bb_exit
         lda   #$0D
         ldx   #$BA
         ldy   #$03
         jsr   modify     ; then set T00,S0D,$BA =
         !byte $6C,$38,00
jmpb4bb_exit