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gsword.cpp: more notes (nw)

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Vas Crabb 2020-04-12 19:55:08 +10:00
parent e4319288dc
commit 761c232d82
1 changed files with 14 additions and 4 deletions
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18
src/mame/drivers/gsword.cpp
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@ -299,8 +299,9 @@ and a value in the low five bits. Instructions recognised are:
* 0x60: Set coin 2 coins per credit ($3D, default 1)
* 0x80: Set coin 1 credits per coin ($33, default 1)
* 0xa0: Set coin 2 credits per coin ($3B, default 1)
* 0xc0: Set value at $2A (default $08)
* 0xe0: Swap nybbles and set value at $29 (default $80)
* 0xc0: Set protection delay ($2A, default $08)
* 0xe0: Swap nybbles and set protection time ($29, default $80)
The protection delay is not used by Great Swordsman.
The setup phase is terminated by writing a command to the I/O MCU's data
port. The MCU return a data byte depending on the low three bits of the
@ -322,9 +323,18 @@ byte of program memory from page 2 using the received byte as the
offset, twos-complement it, return it, and then immediately re-execute
the previous command received on the data port.
The protection routine sends a sequence of incrementing values to the
host. The value is incremented by 1 or 2 if its most significant bit is
clear or set, respectively. Every 256 iterations, the value will be
replaced with a byte read from an incrementing offset in program page 3.
The iteration count, protection value and offset all start at zero and
persist between invocations of the protection subroutine. The
protection subroutine runs for a configurable amount of time after each
command is received.
The I/O MCU indicates status via the user-defined status flags. It sets
them to 0000 while waiting for a command, or 1111 while processing a
command.
them to 0000 while waiting for a command, or 1111 while running the
protection subroutine and processing the command.
******************************************/