FreedomFighterNotes
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Contents |
Prototype
Difference in Freedom Fighter VGG board from Star Rider
Patch cable betwween U116 and U117 moved
Moved from pin 4 of U117 to pin 6 of U117. The cut trace under the word "U117" seems to be present on stock Star Rider VGG boards.
U87 mod
Pin 8 appears to have been cut off.
U85 (unverified) mod
I need to double check the silk screen, but I am pretty sure that this is U85. A capacitor or resistor (I am not sure which it is) has been added.
NOTE : I found this mod on a Star Rider VGG board also, so it does not seem to be Freedom Fighter specific after all.
Transistor mods
Three capacitors/resistors are added to three transistors. These transistors are most likely related to the RGB monitor output circuit. My guess is that these are caps.
NOTE : I found this mod on a Star Rider VGG board also, so it does not seem to be Freedom Fighter specific after all.
U65/U84 mod
Pin 8 of U65 connected to pin 6 of U84. Part of U84 pin 6 appears to have been cut off.
U64 pin 6 is VSYNC' (DISK) on star rider VGG schematic 3/5. As the VP-931 player does not provide composite sync, the CSYNC input to VCC may have been replaced by something else for Freedom Fighter and thus the schematic would need to be interpreted differently.
U65 pin 8 is part of disabling the expander. If it is high, the expander is forced to be disabled.
U77 mod
Pin 5 has been removed in order to prevent the expander from being disabled by the vertical line count.
PIF board
ROM program memory map
| Address Range | Description |
| 0xE000-0xFFFF | ROM (The ROM chip is a 27128 [16kB]) but from what I can tell by studying the hardware, only 0xE000-0xFFFF is actually addressable due to the way the 74LS138 is laid out. I can see no way for the rest of the ROM to be addressed at all. |
| 0xC000-0xDFFF | For this memory range, the 74LS138 is connected to a 74LS125, but so far I can't see that it actually has any effect. So for now, this is 'unknown'. |
| 0xA000-0xBFFF | Doesn't appear to be connected to anything. |
| 0x8000-0x9FFF | PIA control. Similar to Star Rider, but not completely verified. |
| 0x8000 | access PIA peripheral register A or data direction register A depending on control register |
| 0x6000-0x7FFF | Read or write to the VP-931's data lines. Goes through a 74LS245. |
| 0x4000-0x5FFF | Doesn't appear to be connected to anything. |
| 0x2000-0x3FFF | Read from DAV/DAK lines (any address should have the same effect). DAV will be on bit 6, DAK will be on bit 7. |
| 0x0000-0x1FFF | RAM (U2, only 2k so memory region repeats every 0-0x7FF) |
