Exidy Fax PCB, ROM/PROM swapable to Venture?

Found a fax dump...

D6 has:
Code:
10010 10110110  ; CSCG1
10011 10110000  ; CSCG1
10100 00011000  ; CSCG1 CSCG2
10101 00011000  ; CSCG1 CSCG2
10110 11010110  ;       CSCG2
10111 11010000  ;       CSCG2

So $4800 maps to either spot for a 6116...
Code:
CSCG1 = ph0b & /vselb & /a11 &  a13  ; 1001-   $6000
      + ph0b & /vselb &  a11 & /a13  ; 1010-   $4800
 
CSCG2 = ph0b & /vselb &  a11         ; 101--   $6800 / $4800

Go figure.
 
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The MAME Pepper II C5 prom appears to map both $4800-4FFF and $6000-6FFF to /VSEL, so that's not an issue.
It also maps $4000 - $43FF to /VSEL which makes your below statement incorrect.
...and they may not even need decode A13 at all since /VSEL takes care of any ambiguity and prevents $6000 writes from stomping on $4000.
Because of above this isn't true. (also I'm not sure why you would suggest that the chip select somehow magically stops writes but not reads from the effected area.)
Found a fax dump...

D6 has:
Code:
10010 10110110  ; CSCG1
10011 10110000  ; CSCG1
10100 00011000  ; CSCG1 CSCG2
10101 00011000  ; CSCG1 CSCG2
10110 11010110  ;       CSCG2
10111 11010000  ;       CSCG2

So $4800 maps to either spot for a 6116...
Code:
CSCG1 = ph0b & /vselb & /a11 &  a13  ; 1001-   $6000
      + ph0b & /vselb &  a11 & /a13  ; 1010-   $4800
 
CSCG2 = ph0b & /vselb &  a11         ; 101--   $6800 / $4800

Go figure.
YES, this is an oddity for sure. What's even stranger is NONE of the data bus buffers are enabled in that $4800-$4FFF so they enable the RAM but don't allow data to flow. I'm not sure what they were intending with this.
 
It also maps $4000 - $43FF to /VSEL which makes your below statement incorrect.
Venture doesn't read/write from $6000-6FFF, so the aliasing doesn't matter.
The point was that $4800 enables the 6116 wihout changes.

Because of above this isn't true. (also I'm not sure why you would suggest that the chip select somehow magically stops writes but not reads from the effected area.)
Where did I make that claim? 6D doesn't enable either 6116 at $4000.

YES, this is an oddity for sure. What's even stranger is NONE of the data bus buffers are enabled in that $4800-$4FFF so they enable the RAM but don't allow data to flow. I'm not sure what they were intending with this.
Which gets fixed by burning over top of the existing 6d to clear 2 bits...
 
Venture doesn't read/write from $6000-6FFF, so the aliasing doesn't matter.
The point was that $4800 enables the 6116 wihout changes.
More wrong information, you are turning this thread into another useless string of nonsense.
If you are suggesting using one prom for all games then the aliasing DOES matter since the 2bpp games use $4000-$43FF for screen ram and $6000-$63FF for character ram.

If you are suggesting using the existing FAX 6D "without" changes for Venture then it still will not work because 5ECGBD is not asserted low for $4800-$4FFF so the '245 at 13B will not be enabled for the CPU to write or read from the 6116

If you are suggesting using the existing FAX 6D and cutting the A13 input and tying it high just for Venture it ALSO will not work because now 5ECGBD IS asserted on accesses to $4000-$43FF which on a read of screen ram will clobber the bus.

Where did I make that claim? 6D doesn't enable either 6116 at $4000.
It does if you've tied A13 high at the prom.

You are throwing out all kinds of random statements that are making it difficult to see what you are trying to accomplish.
 
If you are suggesting using one prom for all games then the aliasing DOES matter since the 2bpp games use $4000-$43FF for screen ram and $6000-$63FF for character ram.
This thread is about converting fax to venture with as few changes as possible, not about making a set of proms work for both games.

If you want him to burn all new proms, swap RAMs, and undo The A13 wiring, then yes that'll obviously work.

If you are suggesting using the existing FAX 6D "without" changes for Venture then it still will not work because 5ECGBD is not asserted low for $4800-$4FFF so the '245 at 13B will not be enabled for the CPU to write or read from the 6116
Hence the comment about clearing 2 more bits in the prom so it does.

If you are suggesting using the existing FAX 6D and cutting the A13 input and tying it high just for Venture it ALSO will not work because now 5ECGBD IS asserted on accesses to $4000-$43FF which on a read of screen ram will clobber the bus.
You're several posts behind and are making poor assumptions.
 
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