|実機資料||低||解決済み||修正済み||2009-01-26 16:48||2009-01-29 18:24|
stactics - スペースタクティクス
|詳 細||The stactics.c driver currently includes the following entry in the main address map:|
AM_RANGE(0x4000, 0x47ff) AM_RAM
This specifies 2 KB of scratchpad RAM. However, examining the schematics and parts lists in the Space Tactics manual, available at:
shows that the scratchpad RAM is implemented with only two 256 x 4-bit RAMs (AM91L11APC, AMD's version of the 2111A) designated as IC152 and IC156. (See PDF page 39.) PDF page 49 shows these RAMs, which are activated for all addresses in the address range 0x4000-0x47FF. PDF page 46 shows the address decoder (IC133) which generates this signal. Address bits A8 to A10 are ignored.
Observing the game from the MAME debugger seems to further support this. Only one RAM location within 0x4100-0x47FF is accessed, but this appears to be simply a mirror of the corresponding location within 0x4000-0x40FF. There is no sign that the program wants to use more than 256 bytes of scratchpad RAM space.
This problem doesn't seem to affect gameplay, since the aforementioned single location is never accessed from the 0x4000-0x40FF range, so there is no aliasing problem. But it does result in an inaccurate simulation of the hardware and is misleading to someone trying to understand the hardware from the MAME driver.