For System 80/80A you need my Adapter, for 80B just change code at Game-Prom

Change to freeplay, first version:
Prevent that credit counter get decremented
change only 3 bytes, all the same for System 80/80A/80B
original code sequence
E9 00 10 02
change it to
18 18 90 02


Change to freeplay, second version:
Credit counter function normally, if counter is 0 and
start button is pressed credit counter goes to max credits
change only 1Byte:

For System 80/80A
original code sequence
A5 42  F0 EB C9 F0 F0 E7
change it to
A5 42  F0 EB C9 FF F0 E7

For System 80B
original code sequence
A5 BF F0 EA
change it to
A5 BF 90 EA

first version, more details ....

SYSTEM 80/80A, code for 'U2/U3 Prom:

curcred at $0042   ???
sbc  #$00     E9 00       # sub 0 AND carry bit from A
bpl (plus 2)  10 02       # if still plus jump to ...
adc $32        65 32    # ??? something with maxcred ???


SYSTEM 80B, code for Game-Prom
curcred at $00bf
 sbc  #$00     E9 00       # sub 0 AND carry bit from A
 bpl (plus 2)  10 02       # if still plus jump to ...
 adc $BE        65 BE     # ??? something with maxcred ???


changed to
clc                 18        # clear carry bit
clc                 18        # clear carry bit
bcc (plus 2)    90 02  # if carry bit cleared jump to ...

second version, more details ....

for SYSTEM 80/80A, code for 'U2/U3 Prom:
curcred at $0042   ???
lda $42         A5 42  # load current credits to akkumulator (it is only low byte)
beq $27B4   F0 EB  # if equal null jump to .. (why?, what is high byte?))
cmp #$F0     C9 F0  # compare with F0, this is if low byte is null
beq $27B4   F0 E7   #if equal jump to ...

changed to

27C5:   lda $42         A5 42  # load current credits to akkumulator (it is only low byte)
27C7:   beq $27B4   F0 EB  # if equal null jump to .. (why?, what is high byte?))
27C9:   cmp #$FF     C9 FF  # compare with FF, this is if low byte is F (never!?)
27CB:   beq $27B4   F0 E7   #if equal jump to ...

for SYSTEM 80B, code for Game-Prom
lda $BF             A5 BF   # load current credits to akkumulator
beq $2C8A       F0 EA   # if equal 0, jump to ...

change to:
lda $BF             A5 BF   # load current credits to akkumulator
bmi $2C8A       90 EA   # if minus (never!), jump to ...



planed for next version:
adjustable with dip switch ( No 1.1?)
adjust checksum


01.12.2005, RTH