F-18 Hornet Absolute Cartridge PCB

[Trebor]

Had a friend inquire about the need of F-18 Hornet PCB pictures. I was unable to find anything readily available, so took a few of my own. Below is a sample of two captures for any interested:

Additionally, the description of the cart type taken from MAME/MESS sources is as follows:

"Carts with Absolute bankswitch:

64K games. Lower 32K are 2 banks of 16K to be mapped in 0x4000-0x7fff, depending on the value written at 0x8000. Higher 32K are fixed in 0x8000-0xffff"

Above information is certainly available elsewhere, but just thought it as a nice accompaniment of the posted pictures.

[phoenixdownita]

If you notice there are only combinatorial 74XX series chips beside the ROM (no flip/flop or latches)

1 74LS32 (quad OR) and 2 74LS00 (quad NAND).

 

Unless the ROM itself has some flip/flop I am not sure how the cart remembers which of the 2 lower 16K bank is actually mapped at 0x4000-0x7fff.

 

In short I believe either the description of it requires special ROM chips (it would be a first for the 7800) or how it works is poorly understood at this stage.

 

[Note, with proper wiring one can use the quad NANDs to implement a rudimentary latch but it seems weird they would do that when the 74 series already offers them (74373 74374 among the others)]

Edited July 11, 2015 by phoenixdownita

[Trebor]

If you notice there are only combinatorial 74XX series chips beside the ROM (no flip/flop or latches)

1 74LS32 (quad OR) and 2 74LS00 (quad NAND).

 

Unless the ROM itself has some flip/flop I am not sure how the cart remembers which of the 2 lower 16K bank is actually mapped at 0x4000-0x7fff.

 

In short I believe either the description of it requires special ROM chips (it would be a first for the 7800) or how it works is poorly understood at this stage.

 

[Note, with proper wiring one can use the quad NANDs to implement a rudimentary latch but it seems weird they would do that when the 74 series already offers them (74373 74374 among the others)]

 

Perhaps this bankswitching guide, by Eckhard Stolberg, helps with the specifics:

 

"F18 Hornet has it's own bankswitching format (78AB). It has 32K of fixed data at $8000-$ffff and 2 16K banks at $4000 - $7fff. The two banks get mapped in by writing either $01 or $02 to address $8000. I don't know if other addresses trigger the bankswitching too, but I'm assuming any address above $8000 might work. I have no idea what happens when you write other values to the hotspot, but they probably will just be ignored."

[phoenixdownita]

It does not help per se.

In order to have the bankswitching work you need a "memory element" that retains the settings in between changes.

My point is that unless such element is inside the ROM, the extra 74LSXX chips seem not to offer such feature, at least not in a std way.

 

For example last year I found out that the actual ROM of Rampage and Double Dragon were wrongly described and had a bad mapping, the official files contains the data swapped at 8K boundary wrt the real ROM which I personally dumped to actually figure out the blunder. When I had to build a dual cart the offical "bin" files for those 2 simply did not work on the actual cart until I swapped the pages. This is just an example to say that known description for those one off games do not always match reality.

 

I did not care to investigate deeper for F18 as I had acquired it relatively cheaply.

 

My statement here is about a non complete understanding of the F18 board. I have not seen a description/schema of how those extra 74LSs come into play and if an integrated flip-flop is responsible for retaining the bank number.

It is instead rather easy to understand what the extra 74LSs chips do in the Atari boards, there's even some schematics around and the flip-flop latches are always in the relative 74LS373/374 chip. Wrt Rampage and Double Dragon their flip-flop is instead integrated into the PAL chip and that too is documented [albeit we still do not have reversed engineered the PAL code itself, my interest in it waned as I used the original Rampage PCB as the base].

 

In any case the pictures are great.

 

Here is the link to Eckhard post wrt Renegade:

http://atariage.com/forums/topic/224038-multicarts-suggestions/page-3?do=findComment&comment=3021105

Edited July 11, 2015 by phoenixdownita

[santosp]

.....and to complete this excellent thread, two naked pcb photos! I don't believe cause anyone (so crazy like me) in the past has done something like this. Thank you Robert.

 

 

Edited August 6, 2015 by santosp

[santosp]

A useful info for anyone need to burn an eprom, as to convert one color version of this game to another, using official - web binary.

On an HEX editor cut hex 4000(h) to 7FFF(h) and paste - insert at the 0000(h). After burn on a 27C512 eprom.

[tpapahem]

The two banks get mapped in by writing either $01 or $02 to address $8000

Edited August 8, 2015 by tpapahem