PSX Gold Finger hardware notes
 (C) 2012 Charles MacDonald

 The Gold Finger is a clone of the Datel Action Replay, which
 uses a hacked version of the Caetla firmware.

 Memory map

 1F000000-1F01FFFF : Flash (first 128K)
 1F020000-1F03FFFF : Status port (bit D0 driven, D1-D7 floating)
 1F020010.b        : Switch state
 1F020018.b        : STB pin from Comms Link card state
 1F040000-1F05FFFF : Flash (second 128K) + feedback area (see below)
 1F060000.b        : Comms Link data input (byte)
 1F060008.b        : Comms Link data output (byte, pulses ACK to Comms Link)

 The AR only supported 128K of flash and reserved 1F040000-1F05FFFF
 for future expansion; accessing this address range caused the PAL to
 pulse an output pin which fed back to an input pin and would have
 allowed CPU data bit 0 to be latched. The PAL is not actually programmed
 to support this behavior, but the hardware does.

 The GS retains the feedback circuit but doesn't use it either. It
 connects CPU A18 to Flash A17, whichs maps the second half of the
 flash to the 1F040000-1F05FFFF range.